I don't know about ico but in alot of games you can increase your d3d internal resolution. Most people use this as a form of aa you just take your monitors resolution and multiply it by 3 or 4 but with a gtx580 you might be able to go higher. I don't know if you can adjust your internal res in ico but in alot of games it's worth it. I just saw your card and was wondering what it could do. If your not that familiar with pcsx2 I would enjoy gaming a little before I help you ruin your configuration but if your ever curious just go into config/ plugin/bios selector next to where you select your gs plugin on the top right click config. Look for D3D internal resolution and in the white boxes manually enter your desired resolution. Then where you selected x6 set it to custom or 1. I would start with something like 1840x2160 then work your way up cause it can crash pcsx2. If you ever wonder plug it in but don't worry about it just enjoy the game really.
That's impressive although when you tell people you have a gtx580 and then tell them your playing maximo you might get some looks. Don't worry it happens. But you should also try dolphin if you have a gamecube/wii.
Hate to be off topic but in mgs3 I get slow down any time on run through grass is and was wondering. Is the swaying handled by the emotion engine and is that the weak link in the emulation. I also get heavy slowdown in gt4 and was wondering if that was the cause of some of it.