1) The PCI-e verison and AGP version will perform identically if they are clocked the same. You just can't compare benchmark results directly from different sites as test system and testing methods vary. If one site reviewed a card and passed it onto another site who put it in a identical system, they still wouldn't get identical results if they used different timedemo's or map areas.
2) The CPU bottleneck is not an issue for you. There are certain games or even parts of a game that may be CPU bottlenecked, but for the most part your max playable settings will be as a result of the 7600GT bottlenecking. Take for instance Oblivion. For the most part you will be completetly limited by the 7600GT, but when near town gates with lots of NPC's in site, then the CPU could bottleneck. Benchmarks like 3dmark05 at default settings will benefit from a CPU boost, but your gaming shouldn't be an issue if you tweak your settings to the best playable. BTW, the 3000+ Winny's are good for an easy 2.2GHz, and the Venices even higher. So if you want to go that route there is a free CPU boost just an OC away. :wink: But IMO A64 3000+ cpu bottlenecking is more an issue for the very highend cards and definately for SLI/Crossfire (2 cards working together). Just not at all an issue for a 7600GT.
Just a thought. You have the perfect system to throw a 7600GT AGP into. Having S939, you also have the perfect opportunity to buy a PCI-e mobo as the 7600GT AGP is hard to find in stock and is $175 if you find it. But a PCI-e version can be found for $110 on Newegg allowing you to put $65 into the mobo. Also, if cost isn't a big concern you could step up to a better card like the 7900GS, X1900GT or even the X1900XT. Just a thought, only you know if you want to bother and know how to reinstall the OS and get a new mobo up and running. For $199 a X1900GT would destroy a $175 7600GT. Even better the X1900XT 256MB for $240. You can recoup costs selling your old mobo. But if $200 is your total budget, I'd say a new mobo and PCI-e 7600GT is money better spent. If the time/labor involved makes that impossible, grab the 7600GT AGP...it's a nice AGP card for your rig. Also, if you have a proprietary system like many OEM computers (Dell, E-Machines, etc.), then you may find the new pci-e mobo route way too difficult/expensive.