I have Turbo On... What I've been reading, especially on evga forum, is that the i7 doens't like even multiplies, so I always try to keep an odd one.

Which doesn't help, because 20 is unstable, and 19 too low.

What are your other voltages? Which PWM are you running on? PCI-E frequency? MCH Strap?

On my first tries I couldn't get 4.0 with less than 1.38V...

Today I use either 4.1 @1.388V or 4.2@1.45

Like you said, HT doesn't seem a big deal to me... It requires a lot more voltage than when it's off. I believe that's one of the keys of achieving a better OC with the i7...

Haven't notice any difference on performance either