GTA 4 probably won't be an enjoyable experience. I have all three games and there is no comparison performance-wise. Dead Space and Mirror's Edge are liquid-smooth at max settings, while GTA 4 is irritatingly laggy at times.
FYI my rig is:
E8400 @ 3.6 ghz
4gb pc 8500 gskill
Asus 4870 1gb (stock)
GTA 4 runs like crap on my system regardless of resolution, shader, or texture setting, but I see some minor improvement when I reduce the draw distance to the minimum. My guess is that the game isn't processing the AI for characters or vehicles that you can't see. The patch that went out on the 23rd of January improved performance noticeably as well. I would think that your graphics card is easily enough for an enjoyable experience on all these games, but GTA 4 is an entirely different animal when it comes to required processing power.