No AA vs AA

I find AA essential for gaming unless I'm using 3D vision. Back in the day, I was happy without AA, but once you get used to it, it's hard to play without AA on. The biggest annoyance without AA on, is that the jaggies seem to sort of move up and down the edges of objects. This is my experience at 1080p and 1200p. At your resolution, it's going to be even more pronounced.

AA will make a big difference, especially at your resolution. Even at 1080p, the jagged edges are still quite pronounced without AA. You don't need a lot of AA at 1080p to smooth the edges out, 2x is sufficient 4x is about as smooth as you can get while still being noticeable, AA will make a big difference even at high resolutions. At 1280x1024 it is even worse, at that resolution, I probably wouldn't play with anything less than 4x AA. 2x AA at 1280x1024 looks like no AA at 1080p.

If you are okay with a lot of jagged edges, the 550 will be fine for your resolution. If you want to crank up the AA, or you plan on upgrading to a 1080p display down the road, the 6850 would be a better choice.

Tnx for your answers, I think I'll go with the 6850  

What wattage does your PSU can supply for maximum?