Jonnyc- checking the list in EFIStudio/UInstaller/OSx86Tools is just a good quick reference: it's likely every (unmodified by a vendor) card on the list works with full QE/CI via EFI strings. Also: double check the (original) OSx86 project Hardware Compatibility List under PCIe cards:
http://wiki.osx86project.org/w....php/HCL_10.5.2#nVIDIA
(Hint: substitute 10.5._ [3, 4, 5, 6] for newer but less complete variations of the list) The PNY 7300GS/256 is on the 10.5.4 list. Disregard most of the older methods people list to get the card working, like nVinject and Natit- I'd refer to the better EFI string method.
By no means is the older Wiki complete, but it's still a great resource. I personally prefer it to the newer one, which is woefully incomplete, and weirdly arranged by manufacturer, making it very counter-intuitive for just quickly scanning working hardware. Using both resources (wiki, and EFI list) you can get a pretty good idea what will work and what won't.
The mouse stutter problem as I recall was related to the AppleUpstreamuserclient.kext file in 10.5.6: once removed, it should fix it. As far as I know, it's not related specifically to the XFX 8800GT, which should work fine.
By the way, for anyone still working on the onboard sound for the GA-G31M-ES2L, use EFIStudio or OSx86Tools, and select AZUL from the device list, and add to the plist. I don't know if you need to re-add the other critical devices at the same time; when I set mine up, I only used EFIStudio to set up everything, not UInstaller.