I have a 2010 Mac Pro and have started shooting vids in 4k. My Mac Pro seems to handle the files without any problem except occasional stutter with horizontal pans. Background renders for stabilisation takes a while, but it's background so doesn't slow down my workflow. Projects are edited on a Samsung 840 Evo RAID that gets speeds close to 1gb/s. I've read that 7970 and 7950 are big upgrades for fcpx. I've tried dual 5770 setup but got a wind tunnel noise with this set up so gave up on it. What practical effect would a graphic card update have?