Mavericks and Radeon 7970 Graphics Card

I have a 2012 Mac Pro Tower and I think "upgrading" to Mavericks fried(?) my Graphics Card. When I was on OS 10.8.4 my Radeon 7970 3GB card worked well. I upgraded to Mavericks and on start up my computer would not go past the grey screen. I tried everything I could, safe mode, PRAM reset and option start to select another boot partition. Nothing I tried got me past the blank grey start up screen.

I still had my stock 1GB Radeon card. With that card installed I was able to boot to the 25GB 10.8.3 second partiion on my 250GB SSD Start Up Disk. I did not want to necessarily erase the 225 GB Mavericks partition. I tried verifying, repairing it etc from the boot partition. None of that would allow me to start up to the Mavericks partition. I eventually erased the Mavericks hard drive partition. And reinstalled 10.8.4 on that larger Mavericks partition. After reinstalling ML all was well on both 10.8 partitions with my stock 1GB Radeon card.

I was curious if the Radeon 7970 3GB still worked with 10.8. Now with the 7970 installed my OS 10.8 no longer starts past a grey fabric screen on regular start up. And nothing past a black screen on option start, PRAM start etc.

To be fair it is not the newer official Mac edition Radeon 7970. There wasn't one when I bought it. Although there were working drivers included on 10.8.4. I think the fact it isn't the MAC Edition 7970 is irrelevant as I have now searched and heard about Mavericks frying other folks stock cards.

I don't know why the 7970 Radeon no longer works at all now like it did with 10.8? I am not sure what is left of Maveicks Drivers etc on my start up disk even after an erase and fresh ML install? I am in the process of verifying the 10.8 start up disk and it looks to be stuck for over an hour.

I am typing on my MAC Pro laptop. I ordered an EVGA Nvidia GTX 770 4GB card to use CUDA with some applications that Radeon OpenCL did not work well with. I am wondering about the current health of my 2012 Tower which was fine and about using the Nvidia card when it arrives?