@ OP:
depending on what model you decide - AGP-graphics PowerMac G5s or the only 3 PCIe G5s introduced October 2005 - you have several options:
if you just want any graphics card upgrade and not want to spend much money (100,-) or wait a very long time or flash yourself the graphics choice variety is bigger for AGP G5s (Dual Processor), if it is to get the best card go PCIe (Dualcore, warning don't mix with Core Duo Intel CPU Macs).
Choices:
http://www.jcsenterprises.com/Japamacs_Page/Blog/4B4B7BA2-7ABB-47F1-87AC-B03D37942BEE.html (see next page also)
SATA-cards PCIe (Mac OS X 10.5):
- out of the box SATA-III card (only working SATA-III that works out of the box)
http://www.jcsenterprises.com/Japamacs_Page/Blog/4B4B7BA2-7ABB-47F1-87AC-B03D37942BEE.html no booting supported, only for data drives or hooking up an ODD
-> 10-15MB/s faster in reading than the SATA-II Digitus card
-> write speads can drop to SATA-I speads
- SATA-II out of the box card (not booting): cards with this board design (the pictured one is made by Digitus)
http://www.hoh.de/images/articles/e6/619581_dabf3e63fee8f82865b4d93d9c913c17_5.jpg from several vendors
-> 10-15MB/s slower read speads than Silverstone
-> faster in writing in general
test results and pictures
http://cubeuser.de/showpost.php?p=21621
(start time for Photoshop CS4 with a 1TB Samsung F3 7sec. over on board SATA-I, the results are from an SSD, so if you want something to open your apps fast take into account that a 1TB drive filled only 1/3 or 1/2 is not that bad here, too.).
bootable SATA-II controller 10.5:
-> see Sonnet (I don't know of PCIe versions from other manufacturers)
-> Delock 70137, flashed with a FirmTek SeriTek/2SE2-E ROM
SATA-PCI/PCIe for OS X 10.4 and 10.5:
- look for (non-Mac advertised) cards with a Silicone SIL3124 or SIL 3132 chipset and if the driver doesn't come with it use these
http://www.drivers-download.com/en/downloadlist.php?id=72 (there is a PCI-X one for 15,-USD on Ebay)
Note: PowerMac G4s and G3s have PCI, but a PCI-X card will work (and physically fit in most cases, look for the gaps to be on the right position. There are only three. They go ----gap--------------
gap----
gap-------, the bold ones are the ones that have to be present, the other doesn't matter).
It will also bring you in real-life 65MB/s (PCI-X and 80MB/s in benchmark tools) over 35MB/s (PCI).
Bootable cards (both 10.4/10.5):
- Macally, Sonnet, Seritek/Firmtek, ACARD
PS: the difference don't look big, benchmarks for different G5s
http://www.macworld.com/article/1047649/dualcorebenchmarks.html unfortunately no Quad in there, but you might find some over at barefeats
this
http://www.macworld.com/product/405718/power-mac-g5-dual-2-3ghz.html notes the fps for Unreal on a 2,3GHz G5 with the base GPU.
I am not sure anymore, but I believe the Dual Cores are a bit quieter than the Dual Processor G5s (when you get an extremely loud one it has often been seen that the thermal compound had dried out, this goes for all models, including the Quad).