Confusion regarding Mac Pro graphic cards I have an eraly 2008 Mac Pro 3,1 and I'm interested in upgrading its graphic capabilities. It currently has an ATI Radeon HD 2600 XT. I have looked online for compatible graphics cards but I'm confused regarding compatibility. For example, the GTX 770 is said to be compatible for the Mac I have if flashed, but I don't understand how that works. Is any GTX 770 available on the market compatible off the bat? Would I need to flash it? Is it possible to keep the graphics card I curently have and add the other one?
Which version of macOS runs on your MacPro? I believe 10.11 is the last version that the cMP3,1 supports... Anyways, if you plan on using the Mojave Patcher I would recommend getting a GTX680. If you really can't live without a bootscreen I would recommend looking at flashing tutorials for NVIDIA GPUs. There are a few on YouTube (esp. GTX680) and macrumors is also a good source. You could also buy a flashed card from MacVidCards, but they are a bit pricey..

I don't miss the EFI Screen on my MacPro 5.1 with an unflashed RX580.

Good Luck!