5850's are DirectX11 too, and 256-bit! The 5850's are great cards but if you want a better power punch, get a 5870. The 5870's have lower clocks than my factory overclocked 5770 but they have twice as many stream processors than my card and is 256-bit, mine is 128. If you choose to go with a 5870, make sure your case can fit it first though. If you want a 6xxx series than you're talking more money, larger size, and higher PSU requirement.:smilewink:
Also there is no point in going with a 6xxx series if that is your reason because all 5xxx series are able to run the same exact drivers as the 6xxx series. Catalyst 11.5 is working just fine for me.