I recently became the recipient of a used Mac Pro 4,1. I successfully flashed the firmware to make it a 5,1 machine. I'm running Sierra with no issues. I have read that you can upgrade the CPUs to better ones. I currently have 2 Quad-core 2.26 GHz processors. What would you recommend for an upgrade? I currently have an ATI 5770 card, which runs great. I boot into Windows 10 sometimes to run Star Trek Online. What card upgrade would you recommend as well? I can run the game at full graphics, connected to a 2560x1440 Cinema Display now, but would love a faster machine for Photoshop as well. I used to have a Mac Pro 1,1, which I also flashed to make it a 2,1. I performed the CPU upgrade successfully and noticed a huge increase in speed. Thanks for the help!