HI Badadam!
“I feel your pain!” (ouch!! do I ever! :-//
With apologies… 
<Rant mode/ON>:
I’ve spent nearly THREE MONTHS chasing after Apple, NVIDIA, ATI/AMD, the http://www.khronos.org source website for OpenCL…
and not the least of it, FOUR HOURS yesterday with AppleCare"support" (ironic quotes!!! bitter irony!!) trying to get ANY straight answers about the availability, suitability, pricing, cabling, power specs of my MacPro “mid-2010” Westmere-6-core Tower… Apple “aint talking”, and practically disavowed me right-out-the-door! (and I don’t look a BIT like Tom Cruise…
Nor is Apple (or anybody!) making any clear sense of what Is (or is NOT) compatible with a MacPro… I can’t even get clear “specs” from Apple as to what the wattage of my MacPro’s power supply is, nor how much of that is available/required to run a “second card” (with the Apple “support” suggesting ONLY another “stock” ATI Radeon 5770 card was acceptable–even though I pointed him to the AppleStore, showing him that Apple DOES have the Quadro 4000 for mac (albeit at a VERY high mark-up over the current “street” price----In Canada, that’s ~$900.xx). One thing! do NOT buy RAM from Apple, unless you don’t mind paying about 400% over “street price” for HYNIX (OEM plain low-grade…) RAM… Apple is very cynically “hosing” customers who don’t know any better, and has been “cheaping out” on hardware components for about 10 years now!. My “stock” ATI Radeon 5770 GPU card that came with my MacPro (14 months ago) lists for $269.xx presently, with a street price of $80.xx… NOT upgradable/flashable to newer version of OpenCL, doesn’t support NVIDIA’s “CUDA” GPU-render support… I’m very disillusioned!
Worse, (if that’s possible!) is that NVIDIA only seems to provide HORRIBLE quality “drivers” for its (one and ONLY! offering) Mac-compatible Quadro 4000.xx I’m told by a professional 3-D “geek” I know who teaches at a DigitalArts college downtown (here in Vancouver.) and who has friends who work at “EA” (Electronic Arts) with professional rendering farms…so these guys are most DEFINITELY “in the know…” that side-by-side, running on equal speed intel CPU’s that the MAC version vs the PC version of the Quadro-4000 card (difference in EFI-boot vs. BIOS boot? that part of the “explanation” i got is gibberish to me, being a non-PC user! that the Mac renders at LESS THAN ONE-EIGHT the speed of the “same” card running on a PC… Supposedly all attributable to “CRIPPLEWARE” quality drivers for the Mac…
Oh yes, I recently shelled out $2500.xx for a refreshed version of Adobe CS 5.1 to be able to run on Mac OSX 10.7 (CS 2 was getting a bit stale… 
Guess what? The hardware-acceleration “promised” by Adobe, requires a working NVIDIA card… (again, presumably if you don’t mind being “hosed” over the price, and getting only about 12% of the promised speed… <sigh>
<Rant mode/OFF>
So, the “workaround” that I’ve uncovered is…
IF you can get an NVIDIA card into a MacPro, with suitable power-cabling, and sufficient power to run it (and APPLE “ain’t talking”—no usable nitty-gritty details from them AT ALL… :-///
THEN You can either “dual-boot” your MacPro using Bootcamp software on a “hard” partition of your main internal drive, with an install of EITHER Linux/Ubuntu? or Win.7 and the Bootcamp “boot-loader” will let you boot as if you really WERE a PC running Win.7—it is a standard Intel-CPU chip, after all!..
OR (I’m told (by various "3D geeks IRL or online…all using BLENDER software…)
running Windows.7 or UBUNTU Linux on an actual Mac HD partition
will actually run as “virtual machines”…either OS set using VM-ware “FUSION” OR Oracle’s Free (Open Source!)
“VIRTUAL BOX” emulation software…
SUPPOSEDLY, “inside” of either of these, the correct drivers needed for an NVIDIA card,
ARE available [for Windows or Linux,] (but NOT for/from Apple!!).
HOWEVER, the “devil is in the details”, and “nobody’s talking”… so, like you, I’m somewhat cut adrift from knowing how to proceed
and what/which if any options are technically or financially viable…
I’ve been a loyal Mac “fanatic” for THIRTY YEARS, and I never thought I’d say this in public, but,
DAMN Steve Jobs, and the horse he rode in on! ;oP
If this “Bootcamp” option doesn’t work, I’m heading over to the local “FREEGEEK” computer-recycle depot and see if somebody there can build me a custom “box” that DOES support Win.7 AND Linux, since I need Photoshop, AND iTunes—which does run on Win.7… If there was (fat chance!!) a Ubuntu version of iTunes, and photoshop? I’d have switch platforms long ago! :-))