i have a pretty good rig.. geforce3, 1.4ghz cpu..
when started playing at 1600x1200x32.. my framerates were fine, but i noticed the distance detail was just too hard to make out.. When a plane is at 4k at 1600x1200, all i see is a single pixel. at 1024x768, a plane at 4k is at least 3 pixels, sometimes more. This makes it much easier to get a read on the enemy. So I don't recommend anything over 1024x768 (which i use exclusively)
kraquen