As you probabaly know some cpu's just plain suck at overclocking!
When i had my Q6600 in a Asus Commando motherboard i managed to hit 3.6GHz but even with my thermalright ultra the temps still hit the 70'c+ mark becasue like u i needed really high voltages.
Personally 70c+ is too warm for me, I settled for 3.2GHz with my Q6600.
Honesly if you wanna Get a decent overclock get atleast the i7 920(looks like you already have a good cooler) .... I have this cpu @ 3.6GHz on 1.1v and its rock solid prime stable, I can it 4.2+GHz and its still prime95 Small FFTs stable but at 4.2+GHz i have to turn multithreading off to get decent temps.
Have you tried enabling Load-Line Calibration & disabling multithreading in this bios?(sorry if you have i havent read all posts)
Good look man.