It would appear from the above that you have a late model PowerMac G5, dual core 2.0 GHz. This is the same generation as my original PowerMac G5, and from its technical documentation, I see that it uses PCI Express (PCIe) not PCI-X. Hence the card that you are looking at likely will not be compatible with your machine.
I think that you are looking for a PCIe Ultra320 SCSI, from what you say, like
this one or
this one.
Please don't buy anything without confirming that your machine is PCIe vs. PCI-X, but I think that it is the same generation as my PowerMac G5, so unless you know for sure that it is PCI-X, I think it is PCIe.
PowerMac G5 owners, is there anyone out there with the 2.0 GHz dual core model? Can you comment on whether it is PCI-X or PCIe? It is always possible that Apple put different interfaces into the different models... anything is possible!