***WARNING Long Post, read at your own discretion***
Update on my OC E8400:
Well I'll give a brief review of what I've done and learned with this chip and motherboard. About 3 weeks ago, I bought a 680i board to replace one of my systems, an AMD 5400+ build. Long story short, the only processor that works on that motherboard is my E8200. So I decided to go ahead and pick up the E8400.
At first it was fairly easy, I got the E8400 to 4.05ghz(450x9)@1.27v with breeze, as I used settings from my E8200, and worked from there. I ran 100IBT and 5 hours of Prime95 SmallFTT. Passed no problems. I was stoked, and prematurely annouced here my overclock. Then things started going weird on me.
As overclock stability testing go, I run IBT and Prime95 Small FTT for CPU testing, Memtest85 and Prime95 Blend for memory and system. I started blend testing and it would fail between 30mins-3hours, never got pass 3 hours on blend. The system would not crash, OS wise, but the application would just stop responding. I could shut it down and restart a new one. This is normal, I figure my HT or NB voltage was low, as my memory voltage was set to the proper 2.3v for my Patriot Viper(running at 800mhz).
I slowly raised my NB and HT from 1.44v all the way up to 1.6v. Still the blend test will fail randomly within that time span. I ran Memtest86 and it passed 4 passes. Still scrathing my head, I replaced my RAM to see what would happen. I replaced them with OCZ Fatality 800mhz ram. Same thing. One sure fire way to replicate the problem without having to use Prime blend testing was to run Co. of Heroes. It was guranteed to crash anywhere with 10-30mins of playing.
At this point, I consider an OS driver problem. I dual boot Vista64 and XP Pro, so I boot into XP, load of Co. of Heroes and start playing. Sure enough it crashed. So I'm back to the memory again. I played with timings, mem+HT+NB voltages of varying settings, and mem speed. Thinking it may be my memory slots, I replaced the OCZ 2x2gig modules with GSkill 4x1gig modules. Same thing.
On a hunch, I turn down the overclock to 3.6ghz with current settings. Worked like a charm, 5 hours of blend passed and Co. of Heroes did not crash. This sucks, I was bummed out, because I had such a crappy E8200, that couldn't get to 3.6ghz. So I thought it had to be the board. I did some research about CPU VTT, which is what your HT voltage is used for, thinking this might be part of my bad OCs. CPU VTT, is best left alone and should only be increase if you have memory overclock, which I found that it will help stablize.
After 2 1/2 weeks of testing and non productive gaming sessions, I bit the bullet and played with the one voltage that I did not increase at all during this time, my CPU voltage. I up it a 2 notches to 1.29v and started testing. Blend passed a 5 hour session, so I started gaming testing with Co. of Heroes, that passed also with no problems. I then did Vantage testing and it crashed on my 2nd run. Since my vcore was so low, I increased 2 notch to 1.31v. I'm glad to say that this passed 8 hours of Blend and all gaming tests and benchmarks. I only did a quick 25IBT, seening as it passed 100IBT at a lower vcore, I'm not too much worried about this. This vcore voltage threw me off, since all the processors I've used on this motherboard did not behave like this: P4 530, E2180, E6850, E8200. If it passed IBT and SmallFTT, but failed Blend then working with NB, HT and memory settings usually solved the problem.
Here are my final settings E8400 4.05ghz(450*9)@1.306v
Vcore: 1.30625v(I turned it down a notch for daily use, I think the Vantage crash may have been my video card overclock)