here is 2 pages that can help you understand and make the right choice for a g5
page 1 ram which put in a g5
http://support.apple.com/kb/HT2248
page 2 whether PCI or PCIe and PCIX see all models
http://www.everymac.com/systems/apple/powermac_g5/faq/powermac-g5-number-type-speed-pci-pci-x-pcie-slots.html
attention and avoid the problem of leakage water cooling c the models above 2.3 are water cooling veiled jespre have you help and not say too much btises. (^ _ ^) / ~~