No, the 6990 is very loud not to mention over priced, and also not really worth it compared to a crossfire 6970/50 setup. Unless you can't do a multi-card setup or don't want to.
As far as which 6950 is best; I'd say go with the best deal you can find. I personally like the HiS IceQ 6950 which also comes with a free copy of Grid 3. Actually both of my cards came with two free copies.
please help, as i am using gigabyte 550ti and plan to upgrade to either 6950, 570 or 580, which one is better and does not loud. or should i stick to 550 ti? Thanks
Obviously the 580 is the best single gpu solution. If you can go multicard, then 6950 crossfire or 560 ti sli gives much more than a 580 for the same price.
Also depends on resolution. Anything less than 1080p would be a waste of so much graphics power.
For the money the Radeon 6950 and the GTX 560Ti offer high performance and good value. The value tapers off after that, but if you can aford to buy the best then yes the ASUS Matrix GTX 580 as well as the MSI lightning or Gigabyte Super Over Clock of the 580 are the best you can get as far as a single GPU card.