I decided on my update card this past weekend and picked the X800GTO. But looking today at the order status the X850PRO has shown up as a possibilty. Both the same 256mb GDDR3 but should I return and order the pro. Your help will be needed. Reading specs and reviews it seems the X850Pro might be a little better for a longer time. This is an upgrade to my Nvidia 5200 128mb for a sony p4 3.2ghz with 1.5gb of ram.
Here is the link for both.
I just searched it on newegg. Theres no AGP version of the x850pro. Although it is the clear winner in the situation, if you cant find it, then the x800GTO is the ideal pick. Also consider looking at your powersupply for wattage, amps, rails, etc.