Found out now, that if you use the following widescreen hack for Grandia II (U), the lines vanish, even if you use full Texture filtering. No need for any hw hacks.
Code:
comment=Grandia II (NTSC-U) (SLUS-20194) Widescreen Hack (16:9)
patch=1,EE,0025c6d4,word,3c013f40 //vert fov-
patch=1,EE,0025c7a4,word,3c01bf41 //both fov+
patch=1,EE,0025c6d8,word,4481f000
patch=1,EE,0025c7e0,word,461e6343
//FMV fix (by flameofrecca)
patch=1,EE,20401874,word,42a00000 //00000000 fmv x-position
patch=1,EE,2040187c,word,43f00000 //44200000 fmv right side stretch
//Battle Screen HUD fix (by flameofrecca)
patch=1,EE,201694f8,word,42700000 // "ACTION" font
patch=1,EE,20167f70,word,42340000 // "WAIT" font
patch=1,EE,20167f50,word,423a0000 // "ACT" font
patch=1,EE,20167f30,word,42460000 // "COM" font
patch=1,EE,20168a58,word,42580000 // "Combo" font
patch=1,EE,2016afb8,word,42900000 // "Ryudo" name
patch=1,EE,2016aff8,word,42900000 // "Millenia" name
patch=1,EE,2016afd8,word,42900000 // "Elena" name
patch=1,EE,2016b058,word,42900000 // "Mareg" name
patch=1,EE,2016b038,word,42900000 // "Tio" name
patch=1,EE,2016b078,word,42900000 // "Roan" name
patch=1,EE,20168ab8,word,42b88000 // "Moves/Magic" font
patch=1,EE,20168ad8,word,42640000 // "Defend" font
patch=1,EE,20168b18,word,41a80000 // "AI" font
patch=1,EE,20168b38,word,42460000 // "Escape" font
patch=1,EE,20168a98,word,422b0000 // "Items" font
patch=1,EE,20168a78,word,424f0000 // "Critical" font
patch=1,EE,20168af8,word,423a0000 // "Evade" font
patch=1,EE,20168090,word,41b40000 // "HP"
patch=1,EE,201680b0,word,41cc0000 // "MP"
patch=1,EE,201680d0,word,41a80000 // "SP"
patch=1,EE,20168e80,word,41900000 // star rating icon fix
patch=1,EE,20168f20,word,42580000 // "One Foe/Enemy Line/All enemies" icon
patch=1,EE,20169140,word,41900000 // sword icon
patch=1,EE,201695d8,word,41900000 // Ryudo icon (turn order)
patch=1,EE,201695f8,word,41900000 // Elena icon (turn order)
patch=1,EE,20169618,word,41900000 // Millenia icon (turn order)
patch=1,EE,20169658,word,41900000 // Tio icon (turn order)
patch=1,EE,20169678,word,41900000 // Mareg icon (turn order)
patch=1,EE,20169698,word,41900000 // Roan icon width (turn order)
patch=1,EE,201696f8,word,41900000 // monster icon (turn order)
patch=1,EE,20169e58,word,41900000 // monster icon (turn order)
patch=1,EE,20169758,word,41900000 // monster icon (turn order)
patch=1,EE,20169718,word,41900000 // monster icon (turn order)
patch=1,EE,20169798,word,41900000 // monster icon (turn order)
//Status Effect Icons
patch=1,EE,20169518,word,41900000 // attack up/down
patch=1,EE,20169538,word,41900000 // defend up/down
patch=1,EE,20169558,word,41900000 // act up/down
patch=1,EE,20169578,word,41900000 // movement up/down
patch=1,EE,20168130,word,41900000 // poisoned
patch=1,EE,20168190,word,41900000 // paralyzed
patch=1,EE,201681b0,word,41900000 // confused
patch=1,EE,201681d0,word,41900000 // block magic
patch=1,EE,201681f0,word,41900000 // block moves
//Damage HUD effects
patch=1,EE,20168660,word,42100000 // "Damage" font
patch=1,EE,201684c0,word,41c00000 // "Hits" font
patch=1,EE,20168380,word,41900000 // yellow number 0
patch=1,EE,201683a0,word,41900000 // yellow number 1
patch=1,EE,201683c0,word,41900000 // yellow number 2
patch=1,EE,201683e0,word,41900000 // yellow number 3
patch=1,EE,20168400,word,41900000 // yellow number 4
patch=1,EE,20168420,word,41900000 // yellow number 5
patch=1,EE,20168440,word,41900000 // yellow number 6
patch=1,EE,20168460,word,41900000 // yellow number 7
patch=1,EE,20168480,word,41900000 // yellow number 8
patch=1,EE,201684a0,word,41900000 // yellow number 9
patch=1,EE,201684e0,word,414c0000 // number 0 font
patch=1,EE,20168500,word,414c0000 // number 1 font
patch=1,EE,20168520,word,414c0000 // number 2 font
patch=1,EE,20168540,word,414c0000 // number 3 font
patch=1,EE,20168560,word,414c0000 // number 4 font
patch=1,EE,20168580,word,414c0000 // number 5 font
patch=1,EE,201685a0,word,414c0000 // number 6 font
patch=1,EE,201685c0,word,414c0000 // number 7 font
patch=1,EE,201685e0,word,414c0000 // number 8 font
patch=1,EE,20168600,word,414c0000 // number 9 font
//Ending battle screen rewards
patch=1,EE,20168560,word,414c0000 // yellow "Level" number
patch=1,EE,2016ae18,word,41900000 // "SC" icon width
patch=1,EE,2016ae38,word,41900000 // "MC" icon width
patch=1,EE,2016ae58,word,41900000 // "G" icon width
patch=1,EE,2016ae78,word,42700000 // "EXP" icon width
patch=1,EE,2016ae98,word,42900000 // "Coins" font width
patch=1,EE,2016aeb8,word,42900000 // "Items" font width
patch=1,EE,2016aed8,word,42900000 // "After" font width
patch=1,EE,2016aef8,word,42400000 // "level" font width
patch=1,EE,2016af58,word,41900000 // gold icon width
patch=1,EE,2016af98,word,42900000 // character portraits width
patch=1,EE,2016ac18,word,41280000 // number 0 font
patch=1,EE,2016ac38,word,41280000 // number 1 font
patch=1,EE,2016ac58,word,41280000 // number 2 font
patch=1,EE,2016ac78,word,41280000 // number 3 font
patch=1,EE,2016ac98,word,41280000 // number 4 font
patch=1,EE,2016acb8,word,41280000 // number 5 font
patch=1,EE,2016acd8,word,41280000 // number 6 font
patch=1,EE,2016acf8,word,41280000 // number 7 font
patch=1,EE,2016ad18,word,41280000 // number 8 font
patch=1,EE,2016ad38,word,41280000 // number 9 font
patch=1,EE,2016ac20,word,411c0000 // number 0 spacing
patch=1,EE,2016ac40,word,411c0000 // number 1 spacing
patch=1,EE,2016ac60,word,411c0000 // number 2 spacing
patch=1,EE,2016ac80,word,411c0000 // number 3 spacing
patch=1,EE,2016aca0,word,411c0000 // number 4 spacing
patch=1,EE,2016acc0,word,411c0000 // number 5 spacing
patch=1,EE,2016ace0,word,411c0000 // number 6 spacing
patch=1,EE,2016ad00,word,411c0000 // number 7 spacing
patch=1,EE,2016ad20,word,411c0000 // number 8 spacing
patch=1,EE,2016ad40,word,411c0000 // number 9 spacing
//Icons font fix
patch=1,EE,20169100,word,41900000 // apocalypse icon
patch=1,EE,20169000,word,41900000 // fire icon
patch=1,EE,20169040,word,41900000 // tremor icon
patch=1,EE,201690c0,word,41900000 // fire icon
patch=1,EE,20169020,word,41900000 // wind icon width
patch=1,EE,20169060,word,41900000 // elec icon width
patch=1,EE,20169080,word,41900000 // ice icon width
patch=1,EE,20169160,word,41900000 // wand icon width
patch=1,EE,20169120,word,41900000 // millenia dark moves icon
patch=1,EE,20169180,word,41900000 // bow icon width
patch=1,EE,20169200,word,41900000 // heels icon width
patch=1,EE,201690a0,word,41900000 // healing tear icon width
patch=1,EE,201690e0,word,41900000 // tree icon width
patch=1,EE,20169598,word,41900000 // bell icon width
patch=1,EE,20168e00,word,41c00000 // L1, R1 button icon
patch=1,EE,2016b5f8,word,41900000 // item "herbs" icon
patch=1,EE,2016b678,word,41900000 // item "wound salve" icon
patch=1,EE,2016b538,word,41900000 // charm icon
patch=1,EE,2016b638,word,41900000 // scroll icon
patch=1,EE,2016b658,word,41900000 // diamond icon
patch=1,EE,2016b718,word,41900000 // egg icon
patch=1,EE,2016b698,word,41900000 // bomb icon
patch=1,EE,2016b298,word,41900000 // wand icon
patch=1,EE,2016b3d8,word,41580000 // dress icon
patch=1,EE,2016b458,word,41580000 // "holy crown" icon
patch=1,EE,2016b498,word,41580000 // "royal boots" icon
patch=1,EE,2016b518,word,41580000 // "demon necklace"
patch=1,EE,2016b6b8,word,41900000 // feather icon
patch=1,EE,2016b738,word,41900000 // bag icon "sandman whiskers"
patch=1,EE,2016b4d8,word,41580000 // ring icon
patch=1,EE,2016b558,word,41900000 // belt icon
patch=1,EE,2016b5f8,word,41900000 // "lumir flower" icon
patch=1,EE,2016b5d8,word,41900000 // fruit icon
patch=1,EE,2016b598,word,41900000 // mushroom icon
patch=1,EE,2016b578,word,41900000 // cape icon
patch=1,EE,2016b6d8,word,41900000 // harp icon
patch=1,EE,2016b618,word,41900000 // nut icon
patch=1,EE,2016b0d8,word,41900000 // statue icon
patch=1,EE,2016b2b8,word,41900000 // bow icon
patch=1,EE,201691e0,word,41900000 // lotus flower icon
patch=1,EE,201691c0,word,41900000 // axe icon
patch=1,EE,201691a0,word,41900000 // sword icon
//number font size fix for character HUD
patch=1,EE,2016a2d8,word,41280000 // number 0
patch=1,EE,2016a2f8,word,41280000 // number 1
patch=1,EE,2016a318,word,41280000 // number 2
patch=1,EE,2016a338,word,41280000 // number 3
patch=1,EE,2016a358,word,41280000 // number 4
patch=1,EE,2016a378,word,41280000 // number 5
patch=1,EE,2016a398,word,41280000 // number 6
patch=1,EE,2016a3b8,word,41280000 // number 7
patch=1,EE,2016a3d8,word,41280000 // number 8
patch=1,EE,2016a3f8,word,41280000 // number 9
patch=1,EE,2016a418,word,41280000 // question mark
//number font spacing fix for character HUD
patch=1,EE,2016a2e0,word,411c0000 // number 0
patch=1,EE,2016a300,word,41040000 // number 1
patch=1,EE,2016a320,word,41100000 // number 2
patch=1,EE,2016a340,word,411c0000 // number 3
patch=1,EE,2016a360,word,411c0000 // number 4
patch=1,EE,2016a380,word,41100000 // number 5
patch=1,EE,2016a3a0,word,411c0000 // number 6
patch=1,EE,2016a3c0,word,41040000 // number 7
patch=1,EE,2016a3e0,word,411c0000 // number 8
patch=1,EE,2016a400,word,411c0000 // number 9
patch=1,EE,2016a420,word,41100000 // question mark
// number font size fixes for Magic/Attack Menu
patch=1,EE,2016a0d8,word,41100000 // number 0
patch=1,EE,2016a0f8,word,41100000 // number 1
patch=1,EE,2016a118,word,41100000 // number 2
patch=1,EE,2016a138,word,41100000 // number 3
patch=1,EE,2016a158,word,41100000 // number 4
patch=1,EE,2016a178,word,41100000 // number 5
patch=1,EE,2016a198,word,41100000 // number 6
patch=1,EE,2016a1b8,word,41100000 // number 7
patch=1,EE,2016a1d8,word,41100000 // number 8
patch=1,EE,2016a1f8,word,41100000 // number 9
patch=1,EE,2016a258,word,41100000 // "times" font
patch=1,EE,2016a2b8,word,41100000 // "minus" font
Don't forget to activate widescreen hacks and 16:9 in GS window. If you want to play in 4:3 (w/o ws hack), the Align Sprite Hw hack might be a better solution, than deactivating texture filtering. I was using the native scaling option before, mostly x3-x4.