Why not check the thread on how CUDA and 3D work with GTX?
Release October, for $2,249
Or, how can Barefeats or anyone tel until it ships? can't really say can we.
http://www.barefeats.com/rogue02.html
http://www.barefeats.com/rogue01.html
There are those who pay extra to have GTX 570 flashed PC card to boost CS6 wtih CUDA.
http://forums.macrumors.com/showthread.php?t=1366650
http://myworld.ebay.com/macvidcards/
Juice Mac Pro Photoshop w/ video card:
http://forums.macrumors.com/showthread.php?t=1365904
Fastest GPU Mac Pro with EFI Support (the GTX 570 discussion)
http://forums.macrumors.com/showthread.php?t=1360927
- jump to the end of the thread first, then go backwards
Barefeats: Photoshop CS6 Graphics CUDA OpenCL
http://www.barefeats.com/aecs6.html
Maybe this will help make up your mind. Timing and budget
http://www.barefeats.com/aecs6.html
the GTX 670 is going to be a really well valued video card.
http://nl.hardware.info/nieuws/27582/point-of-view-heeft-geforce-gtx-670-gereed
http://www.tweaktown.com/articles/4710/nvidia_geforce_gtx_670_2gb_video_card_per formance_preview/index15.html
The GTX 570 2.5GB was the one recommended with its 2.5GB VRAM. $349.
As Condi said, you pay for support and maybe hope for drivers though Quadro on Mac has not always ever been totally stellar.