[Steve Cohen] “We received a new Octocore G5 from the Apple store back in March when they were unable to repair our Quad-core system. “
A small point: your system is a Mac Pro (Intel), not a G5 (PowerPC). G5s are no longer made.
[Steve Cohen] “I am looking at replacing our last remaining duo-core system and I was wondering if this card (ATI Raedon HD2600) is fine or should I spend the money and upgrade to the NVIDIA GeForce 8800 GT 512MB [Add $150.00]? “
If you upgrade, don’t get the nVidia. Get the ATI Radeon HD 3870. Its performance is superior to the nVidia card in Core Image applications like Motion. The nVidia is a better gaming card, but not as good as the 3870 for the Pro Apps.
https://eshop.macsales.com/item/ATI%20Technologies/100435928/
Performance details here:
https://www.barefeats.com/harper16.html
As for RAM upgrades, there is no advantage to buying Apple RAM. Buy from Crucial or Ramjet and save a bundle.