they are just different, yet to be seen which is better. one review i've seen, forget which one unfortunately, had both a 965 and 975x both tested with same chip, there were a couple benchies where one would be 2-3% ahead, and another test where the other one would win by the same amount. but most were within error margins between them.
yet to be seen which might overclock furthest or more stably. there might end up being little difference between the chipsets. people are working on a 975/965 tweaker just like there was between 865/875 chipset. at the moment a conroe boots in with a 1066 strap, essentially it sets a certain divider to set the northbridge speed and also sets mem controller latencys tight or slack. if you use the 1333 strap you can overclock higher as it will set a bigger divider meaning the chipset won't be overclocked as high, gives you more fsb overhead, but it slackens timings and does cost performance clock for clock. so at the moment the idea is to get the fsb overhead but retighten the timings using a tweaker. not sure if the timings are even tighter at the 800fsb strap, might be able to increase performance even further.
) would like to give me one of their X6800s 