I updated from my 9800GTX which was virtually unplayable to one of Overclockers ATI 6950 2gb, its a VTX brand and i now run everything on High except for buldings detail and buildings amount which is set to medium i also run grass,shadows and roads as well and get around 30fps at takeoff and just after and a good 50fps up high in a dogfight or 45ish fps against bombers and its super smooth with no stutters and very playable. Post Beta i have lost around 5fps. Havent tried the Nvidia card so can't help there but i am well chuffed with this card for the price
Rest of my set up is
AMD 965 quad core processor
8gb ddr2 800 ram
Fatality sound card
750 watt Overclockers own power supply (you need two 6 pin connectors for this card)
One thing that has happened since i got this card is that when i play Bad Company 2 and initially join a game i get a 20 second freeze then its ok for the rest of the time.