Sorry for necroing an old thread but I just want to give an update on the above.
I found that ticking 'Allow 8-bit textures' prevented the slowdown in some areas and caused it in others, depending on what was happening on-screen, as opposed to being a magic bullet that solved the problems completely.
It especially seemed to matter most when the game is rendering a large number of actor models at once, such as the Seagulls by the fence when Raiden gets outside for the first time, or the soldiers watching the screen during Snake's Tanker scene.
While reading another thread here just today (
http://forums.pcsx2.net/Thread-Bug-Repor...rty-NTSC-J ) I saw the tip to change the VU settings for this game and decided to try it out.
I disabled all speedhacks and switched to :
VU0: SuperVU Recompiler (Legacy)
VU1: MicroVU Recompiler
Initial testing suggests that this allows a consistent, smooth framerate regardless of the 8-bit textures option, or even any other gsdx settings; which is quite amazing.
My current system specs for reference:
Core i7 920 @ 4GHz
6GB DDR3
nVidia GTX 580
I'll play on some more and re-test the other problem areas (the fight with Olga on the tanker, particularly) and post back if I find anything else.
Thanks to
Shadow Lady for the VU tip.
Attached screenshot is one of the areas that previously gave huge slowdowns for me (ie; from 120fps down to 25fps), now running in at a steady 50fps with GSDX DirectX11, 1200x1200 internal res, texture filtering on, 8-bit textures allowed.
PCSX2 is an incredible feat of coding, major kudos to everyone involved.