Welcome to TechIMO yanks!!!!
What are you going to be using the G5 for?
If are going to be doing some heavy 3D design and drafting, then i would guess you would see an imporvement with the 9800. But if are just going to be doing Graphics design with Adobe stuff or similar software, then the 9600 should be plenty.
Good luck and let us know how you like the G5.