ATI 5770 has terrible performance... drivers are broken in 10.6.8

On a MacPro stick with 10.6.8 unless you don't have a choice.
OS 10.7.x does work with M364

M364 should be fine on any version of OS.

GTX480 works on 10.6.8 and 10.7.x
GTX570 may only work on 10.7.x - but this is still TBC
Both GTX480 & GTX570 are PC re-flashed cards - so use at your own risk & do test.