I borrowed a used 2006 Mac Pro from PowerMax.com. I installed the Radeon HD 5870 from our Westmere 6-core along with its boot drive. It booted up the first time no problemo. I tried the Mini DisplayPorts with and without the MDP to DVI adapter. Works fine. Right now I'm running game benchmarks on a 24" LED Cinema display plugged directly into the MDP. OWC techies have the 5770 running in their 2006 Mac Pro but could not get the 5870 to boot -- black screen. They are investigating what's different about their 2006 from the one I'm using.