"(Early Mac Pro Cheap 8-Core Upgrade)
I'm kind of late to the game, but I upgraded my Mac Pro 1,1 (2006) 4-core 2.66GHz (two dual-cores) to 8-core with 2 Xeon X5355's at 2.66GHz and I doubled my track count in Logic Pro, pretty cool for $60! (Ref: Intel X5355 CPU info.) I left it at 1,1 (EFI firmware/bootrom), it "gray screened" once at first, but it seems fine now.
I'm staying at OS X 10.6.8 because audio apps just work better there and I have older software that won't be upgraded that I still want to use. (I understand completely - Snow Leopard was the last w/Rosetta support. Although some software requires later OS versions.) Lots of new audio/recording apps still work fine with 10.6.8, they seem to recognize the problems with 10.7 and 10.8.
When the price goes down, I may put 3GHz Quads in there now that I see how well the 2.66 quads work, and get another boost. It was a little weird but not super hard putting them in.
-Robert H."
