Doug,
There was no 5770 2.5 yrs ago which would have been not 2011 anyway but Early 2009.
For us, Apple was still selling that over priced dust bunny clogger X1900 $399 yes.
The 5770 from Apple has always been ~$249 + s/h - and at the time ATI had just cut the PC versions from $220 or so down to $120-150 so a lot of people (summer 2010, the 5770 supply for upgrades did not start shipping unitl... just two years ago, October 2010 after they caught up with new Mac Pros.
I paid $279 for the 8800GT for MacPro 1,1 series - that was around the end of 2008 which was end of when they were available - supply availability died up and of course those have the infamous "bake in oven" if the solder goes bad.
Too bad we never had something like the GT120 $129 but even those have trouble in Lion + if there are two present.
Right now, IF you had a 2010 model and 10.8.2 then there is support for GTX 550 up through 680, even GTX 460 which I have. You may pay same or more but a lot more card and performance.