For persona3 game is best play that game in directx.10 mode with gsdx.0.1.15. I still need vu skip in option to play that game at.50fps and above with my cpu AMD X2 @3.1Ghz and Gpu HD.3870 or You can try vu cycle stealing in option with latest pcsx2 beta r.1059.
I have xenosaga eps.3, this game need gsdx.0.1.6 or gsdx.0.1.7 to play in good speed but you have to play this game in os vista (directx.10 mode) and vucycle stealing is working well in this game.
My computer isfairly similar to yours. A couple of RPGs I recommend that I can also run pretty well are
- Tales of the Abyss, which runs at full speed 95% of the time. The only slow down is when you are walking around in certain spots of different towns. And this is without using the new speedhack, which could probably make even the towns run at full speed.
- Dark Cloud 2, I haven't gotten too far in it, but the first dungeon runs at full speed, the town seems to run mostly at full speed as well (it lags a bit near the circus tent, and maybe a tiny bit elsewhere). This is also without using the new speedhack.
Oh and both of these are using DirectX 9. DirectX 10 could probably run them even better.