I wanted to keep mine below 1.3v so that it wouldn't degrade the chip very quickly. I remember reading an article where a Wolfsdale Core 2 Duo burned out after only 6 months at 1.4v, and they recommended <1.3v or it could degrade the chip in less than a year. I don't know if this holds for the Core i7, but I didn't want to take the chance.
So, I'm sitting pretty at 4.2Ghz at 1.2975v, one step below 1.3v on my P6T. It's perfectly stable running everything I've tried so far. (I started at 4.0Ghz and tried going down as low as 1.25v and stability testing, raising it one notch at each failure, and eventually evened out at 1.2975v at 4Ghz, then ramped up the speed until it became unstable again, dropped it back down one notch, then stability tested it for 24 hours. You see my results.)
I keep my i7 at 3.8ghz to ensure voltage is low at 1.224v otherwise 4.0ghz is not really stable unless I go 1.31v, I can boot 4.0ghz at 1.27v but not that stable. So I do think you are being stingy on the voltage.
However you might end up with the same clock I am using because I think the voltage increase is simply not worth it.
Also setting your RAM timmings highers than the spec wouldn't cause any instability at all.
Your RAM default to 9-9-9-24 because that is what your SPD chip tells your computer to. Officially there is no ddr standard for memory faster than 1067 mhz - therefore the bios will use the standard timings for ddr3-1067 unless told otherwise by an overclocking profile like xmp.
I need 1.3v to run 4ghz, so I too think your vcore is the issue.
@ dgingeri : My best friend has an e6400 (2.1ghz) that he purchased in december 2006. It ran 3.2ghz @ 1.45v for a year until he got a better cpu cooler (tr120 instead of zalman9700) and has been running 3.42ghz @ 1.5v since. The computer's turn on for an average 10 hours a day and at times it has been running wow and other games for weeks with barely a break. I think electromigration is overrated.
Thanks for the responses guys. I'm going to up my VCore a couple notches and see what happens. I'd rather not be anywhere near 1.3. In fact I won't be. I had it running fine at 3.8 at the standard 1.2 VCore, so I wouldn't think I'd have to up it that much to get 4.0, but if I do 3.8 will have to do.