Mac Pro 1,1 models aren't exactly ideal for running Resolve, for the following reasons:
1. The only officially supported CUDA cards for Resolve are the GTX 285 (no longer made) and the Quadro 4000 (expensive) - and neither one of them will function in a 1,1 machine (both cards need EFI-64). ROM chip/firmware-hacked GTX 460/470 cards are also known to work (unofficially). But again, these need EFI-64 and they will NOT work in a 1,1, which is EFI-32.
2. The ideal setup for Resolve is one graphics card for running the GUI (a cheaper, less powerful card like the GT 120, 5770, etc.) and a separate CUDA card dedicated to GPU processing (GTX 285/460/470, Quadro 400).
Now, you CAN run Resolve with just an OpenCL card but it's not nearly as fast and you lose the noise reduction features (which require a supported CUDA card). The cheapest way to go here would be to buy an official 5770 card from Apple or flash a PC version.
With that said, 2008 (3,1) and above Mac Pros are much better platforms for running Resolve properly.
FCP X will work on practically anything that supports OpenCL, including the 8800 GT. But do note that the 8800 GT is a pretty dated card by today's standards. It makes a lot more sense just to get a 5770 which is both faster and more readily available.