For some reason I have never been able to get a ATI cards to work on my computers.
I dont know what it is, as every time I try the drivers will either not work at all or not work properly and cause crashes and other issues.
I even had someone I know who works with these things on a daily basis look at it and even he eventually gave up getting them to work.
As a result I avoid ATI cards like the plague.
My current card however is a GeForce GTX 560Ti, also known as "Phantom", with 2 GB of ram.
The GPU isnt all of course, but still I have never seen my FPS drop below 50 even with heavy action going on the screen, and thats with all settings at max and a resolution of 1650x1080.
Though the card may still be a bit pricey depending on your budget.