My first E6600 died on P5W-DH. I believe the E6600 was from one of the first production batches (but not an ES). Admittedly I literally tortured the CPU for the first two months (like, Prime95 running 20 hours a day) but max vCore I gave was 1.55V (1.52V after droop). It ran great @3.6GHz for a few weeks, then it started degrading. Once it failed @3.6GHz, it wouldn't sustain 3.5GHz shortly after, then from there on it was a downhill pretty quickly. I tried to improve cooling (I turned my room to an igloo) but it didn't help. It stopped working while I was playing with Quicktime video - screen black-out, fans running, etc. At the time of death, it was @3.3GHz. And eventually the board died, too, the following week. I am not sure which one killed which, but I didn't mind much because I was in awe of the performance of Conroe at the time. I forgot about it rather quickly. I remember at least two other users reporting wrt degrading Conroe sometime after, however.
On the other hand, Q6600 was a totally different story. It took a while for me to figure it out.. and much aggravation. It's a long story but the max vCore I gave was 1.40V (possibly 1.42V) and temp was rarely over 60C (lapped TRUE FTW). Let me just say that the whole episode contributed to my general disrespect towards MCM quad-cores. 😀
Oh and despite all the misery I went through with 680i, I don't think it is directly responsible for the Q6600's death. (Though I can't be 100% certain because I had used like 4 different boards until I finally learned of the CPU gone bad)
