pAce I had all the exact questions that you have. I almost made this same post myself! Someone please answer the question, which is more important memory interface or clock speeds? And the reviews I looked up basically says the 6600gt wins whenever the resolution is bigger than 1024 x 768, which I never use anything bigger than this anyway! In some cases the radeon 9800pro outperformed the 6600gt in smaller resolutions! And the AGP version of the 6600gt is harder to find, particularly on eBay. Mostly all I play is HL2, CS Source, and DOD and I dont know how the 6600gt performs in any of those. I don't really give a crap about DOOM.
You can also overclock the 9800pro to XT very, very easy apparently. Someone answer our questions! By the way the x700 isnt out in AGP is it?