you have to be careful though depending on your CPU, without the right amount of memory and the speed, you can bottleneck yourself pretty well.
Though i think most people just go with "pack the fastest you can, and as much as you can" ... it doesnt cost too much more !
But I will say that when I played Skyrim with full specs on 8GB, sometimes (not often) I had slight lag. Mostly choppy screens, so I would just stop running for half a second and let it buffer again.
edit: NINJA'D! LOL
1900x1280. I was playing around and maxed out all the specs. My 570 is good, but not THAT good. so I tweaked a little bit and found the sweet spot. Sorry, I should have mentioned that first.