If you're going with the new Intel LGA775 systems, one thing to note is the PCI-E bus frequency floats along with the FSB. This is part of Intel's overclocking "lock." Mobo makers have found ways (at least partially) around this by manipulating the PCI-E frequency at boot. In all the tests, ATI's PCI-E X800's have been able to handle much higher FSB speeds than NVidia 6800's.
For example, in the latest Intel 925x mobo roundup over at AnandTech, they were able to get a 280 FSB (using a ES proc of course) with an X800 and an Asus P5AD2 mobo but only a 258 FSB using a 6800 on the same mobo.
I was originally interested in LGA775 when it first came out, but I realize more and more that Intel is trying to market new technologies because they're hitting a wall when it comes to clock speed increases. However, the industry may not have a need for these new technologies (yet). It will be a signifigant amount of time before the bandwidth of AGP 8x is fully utilized.