The point of creating this machine was to provide the ability to fit 3 double slot Graphics cards into a Mac case. A Mac Pro was out of the question as with 2 DVD drives and a power supply up top - there is no way this can be fitted. However, the G5 has the space but lacks the quantity of slot outlets for the 7 PCIe sockets on a Asus P6T7 Mainboard.
Once again, my old friend the CoolerMaster "Wavemaster" Case provided the mounting for the Mainboard.
To run at 4 gigs on Aircooling would also require a fairly meaty heatsink, I looked around and the Coolermaster V10 seemed to fit the bill - this thing is massive and incorporates 2 x 120 mm fans!