What do you have it set at now? My E6600 has the voltage set at 1.35...that's what it was when I put it in. I never changed it, but everyone else has the voltage really low.
At 3.4ghz, I have my vcore up to 1.46. As far as stability for me...well, one thing lots of guys here wont ever mention is the fact that ambient temps plays a major role when it comes to oc. Some guys will brag and post their #'s but they will never mention ambient temps. Example, since I've oc'd mine to 3.4ghz, orthos won't last but 10 min. Wait, here's the reason why though, I live in bakersfield, CA and it has been very very hot. I'm cheap so I tend to turn on my a/c only at night. So If i'm on the pc during the day, I'm working with ambient temps of 30.5c. So imagine trying to run orthos under those temps? However, my comp has yet to crash or freeze during my pc usage. I consider that stable. Who the he11 runs ortho type apps all day long? Even during video encoding my comp is stable.
My point is this, if I lived in alaska and ran orthos, I guarantee you my pc would handle orthos. Ambient temps is important. Oh, another thing, some guys will post their cpu speed but it's a one time speed. They don't run their pc at those posted speeds 24/7. Just a one time bragging speed.
One last thing, there are several guys here on tech forums that thought I was b.sing.
I went as far as posting a video to prove them that I was at 3.4 with stock hsf.
Anyways, good luck. up your voltage.