I runned my E6600 during 8 month at 1,5 on air 3,6Ghz, the only reason that stops me with Q6600 quad is that i'm on air, soon as the thermalright ultra arrives will see, as i on summer i got more than 26 ambient so in winter it's my best shot

Till 1,5 it's safe and more with Water Cooler, but i think that it'll take much vcore to be prime95 stable...

Regards Sergio