Most likely your mothboard had to relax your memory timings in order to OC the ram to keep up with the FSB. In case you don't know the math
Speed = multiplier x (FSB/4) on core 2 chips (e6750 has a 8x multiplier)
so at 3.2 Ghz you had a 1600mhz FSB which was perfect for you ram 400 x 2 for being double data rate then x 2 again for being dual channel gives you 1600mhz for memory band width. I would keep it at 3.2 personally.
at 3.3ghz the fsb will be 1650mhz so to keep the ideal 1:1 ratio between ram and fsb the system oc'ed the ram.
thanks. i understood the math as far as the 1:1 ratio and cpu fsb works and did also agree 3.2 was perfect since that puts the ram exactly where it is rated, however i wanted to push the cpu and just see what it could do on stock voltage (3.2 is an OC without changing the vcore). unfortunately 3.3 failed prime95 so i imagine i needed to up the voltage. in the end i agreed with you and that upping the voltage and increasing the timing of the ram wasn't really what i wanted to do for just the little extra bit of power. so, 3.2 it is. still not a bad OC on that chip (20%), especially with stock voltage.