I'm perfectly sure all Q6600s can do 3.6GHz, my point is is that there is a larger percentage of them that cannot do it COMFORTABLY... there is a point on every chip where the scaling is so bad that it's not worth it to pursue higher clocks.
I would say anything over 1.5v not very "COMFORTABLE".
There were lots of threads about people buying L80x batches and getting absolute crap chips that needed insane voltage for 3.6GHz up until L808.
There is no 100% again, as there are good chips in generally bad batches and horrible chips in generally good batches.

What I am saying is based off of personal experience and the experiences of others here... And I can assure you that I am VERY patient in BIOS. I test out every variable possible to narrow it down to the chip.

I think that you need to read some more about the experiences of Q6600 users here before citing lack of patience, experience, or adequate cooling as the reason people can't get 3.6GHz. I bet my first chip could do 3.6GHz @ 1.55v... would I be willing to run that even if I had water? No.

If you want examples of bad chips that would refuse to clock, look here:
http://www.xtremesystems.org/forums/...d.php?t=196981
http://www.xtremesystems.org/forums/...d.php?t=196648