A respectable retailer told me this about putting the 5770 in my 2006 dual 2.66:
“Your Mac Pro 2006 only has PCIe 1.1 and will not be able to run the Radeon 5770 card. There are no good options for the 2006 Mac Pro at this time for upgraded graphics, sorry. Anecdotally I have heard of people being able to install the 5770 in a 2007 Mac Pro after upgrading to 10.6.7 but there is very little in the way of documentation that I can find regarding your exact situation.”
…but, it sounds like it’ll work? Man, I’m confused. I want to run FCPX as well and need the open CL. BTW, it will NOT load off the app store. I get denied. This is why I’m looking into the 5770