I have the same processor and motherboard and was able to reach 3.3 GHz before I started having to really tweak things. If you have GO stepping on your E6750, you should be able to raise the FSB up to 413 and set the multiplier at 8x and leave the core voltage at normal run with no problems assuming you have proper cooling.
i got 3.2 and its running stable, change the fsb to 400 change the voltage to 1.4 turn speedstep, c1e and all other cpu powersaving devices off. Bingo! run prime95 and leave it alone for 24hours after that i say its stable. make sure ram timings are 5-5-5-15 or better else otherwise it will give error.