seeing that your ram timings default at 5-5-5-18 for 400 mhz, i would say loosen them up a little more (something like 6-6-6-20....man that is loose) or lock in the ram at the frequency it is right now. is that the cheap kind of ram? if so....that's probably you're problem. so yeah, lock the frequency of the ram, or try loosening timings. your c2d shouldn't be maxing at 2.8 ghz, and a p965 should get higher than 410mhz fsb. oh and try going ~50 mhz higher (take a jump) i read the bootstraps matter alot.
for instance, if you have your fsb at x mhz it's at x timings (it was new to me that nb's have latency timings or something like that, but it makes sense). at certain fsb's the nb can't go any higher without loosening timings (only accomplished when hitting a certain, higher fsb)
(ps im not sure, but this could be from another chipset, but im pretty sure this applies to all chipsets)