We know, that in game-playing world there are 2 titans — NVIDIA and ATI, pushing bar higher and higher. In Folding world the is one king only — NVIDIA. ATI cards are powerful on paper, but in real (folding)life they lag behind.
Here is quite useful table to choose right GPU card for folding:
Having ambitious plans, there is currently only one way to go — GTX295 double card. In the table only 1/2 card PPD performance is shown. Other cards are single GPU cards and allow max 4 GPU conf’s, as GTX295 doubles one rig capacity.