yea the 6800gs BANGS OUT THE 6600gt. although i would only buy a 6800gs for what it can possibly can do as in overclocked very very hi to come close to performance of what i have now.
The reason they AGP version appears 'underclocked' is because they're not even using the same graphics processing unit. It is equally as powerful as the PCIe version, so don't get your panties in a bunch.