Hello there, I just purchased a used 2008 model mac pro 8-core mac tower for our church with a GeForce 8800 GT card in it. We want to use it for editing video of our sermons. Would I notice much of a difference (upgrading) - replacing the GeForce 8800 GT card with the nvidia GTX 285 card? Please let me know. Thanks a lot for your advice and help.

Just be sure it's a CUDA based card for PPro, and has at least 1GB of VRAM on it.