Hello, I am new in the Mac Pro community. I bought yesterday a 4,1 Mac Pro 8core. I have OS 10.9.5 and tried installing nvidia 660gtx OC but there is no boot. When I install the ATI Radeon HD 4870 512 MB, which the Mac pro came with, it works perfectly. I am a filmmaker and I have a deadline. My old Macbook pro died when I was editing and I bought this Mac for the rescue but this Mac is no use to me without a better GPU. Please does someone know the solution?