A representative from NVidia provided comments and details about their graphic cards and support for Snow Leopard. There are 10 models: GeForce 9400M, GeForce 9600M GT, GeForce 8600M GT, GeForce GT 120, GeForce GT 130, GeForce GTX 285, GeForce 8800 GT, GeForce 8800 GS, Quadro FX 4800, and Quadro FX 5600. They are all compatible with CUDA, but also with Open CL. On the other side, ATI/AMD only offers 2 graphic cards supporting Open CL: Radeon HD 4850 and 4870.
This difference between both companies can be explained by the choice of technologies. When a Mac sports a GeForce, open CL works via a CUDA filter. For the Radeon, codes are only properly translated by some specific circuits found in series 200 and 3000 of Radeon HD 48x0. This difference can explain why GeForces currently offer the best performance level with Open CL. If you want to have additional details, you can read the excellent article from Netkas: http://netkas.org/?p=182.
It indicates that one could boost performance of current Radeon, but Apple and ATI/AMD would have to work together, and it is unclear if the gain would be worth the effort to be invested.
