Do not forget Apple loves to make new hardware incompatible with older hardware. My Mac Pro can not run newer video cards. My only thinking at the time, is that GPU's become too slow over the long term, CPU is just fine still. We'll they prevented me from using the new cards even though they'd run fine in Windows on the same hardware.
So I went out and built a more powerful machine than my Mac Pro, and I dont have to buy shiny new video cards, I just go SLI with a second one of the type I bought with the machine I built. Then upgrade to a new shiny card, when a single model blows my SLI pair out of the water.
I went with Linux, then Mac, then back to Windows 7. What I have learned, you can use anything and make it work, but Linux shines for servers, Apple is a trap to be avoided, and Windows has finally gotten their act together.