It shouldn't run too badly. Just don't expect maximum settings at 60FPS constant. With my rig (see sig) I get between 40 and 50 FPS in GTA IV most of the time, if things get really dense on screen it will drop into the 30s. This at 1080p resolution, with graphics settings on high. Don't increase the draw distance though, that will really kill your performance. Make sure the game is patched to at least version 220.127.116.11 too. Unpatched GTA IV runs horribly regardless of hardware.