Okey, thanks for the heads up man, i'll try my luck first @ 4.0 and push it up a lil bit until I can get it stable to 4.2 (or maybe 4.4) while monitoring the temps on idled and on load.
I'm sorry but I was unable to perform such a task due to the fact that I don't have GTA4. However, I'm quite sure it'll run GT4 smoothly (on max settings) for as long as you've got a really good set RAM and CPU.
I'm using custom skins for this game but only for the ak74u and m4 aimpoint. You can d/l it @ fpsbananadotcom