Hi there. I have a mac pro 1,1 with the default 2 x 2.66 GHZ Dual-Core Intel Xeon CPU. I'm thinking to upgrade it and want to know how far can I go. I've heard 2x 2.66ghz quad core Intel 5355 would be the way to go, but I want to know if I can get something faster for this mac pro. Any help on this would be awesome. Thanks!