I was not aware 1.39vcore was a high oc. According to people's advice I bought high quality components for each part and have failure when my and budget build with 20$ psu and 60$ mb didn't fail for 8 months under dangerous voltages. I wish I could find out how this happen because I don't think I can return parts again.
Your problem sound more like the MB than anything else. It's possible the MB was of marginal build quality and would have lasted years if run at stock speeds the whole time.
When overclocking a person is pretty much rolling the dice on longevity and stability. Pretty much failure can occure at any time.
Your 2600K seems to be above average for overclock vs vcore. I do agree with others that prime isn't enough to trully call a overclock stable tho. But in your case I don't think the is your chip trully stable plays a part in your situation.
What kinda settings did you change on your MB for your 4.8ghz overclock? Maybe something you changed put some xtra stress on the MB which caused it's premature demise.
Just wondering about what you changed. Some of those guides are pretty crappy and seemed to be focused on forcing an overclock on the K chips. Some of chips don't need the xtreme settings they suggest.
Judging by your 4.8ghz at 1.39v's it doesn't look like your chip needs forced overclocking if it's trully stable. My 2700k will do 4.8ghz in the 1.36-1.37v's range.
Power supply wise. I doubt the power supply caused the issue at all. I do agree with others that maybe you should step up a little higher in the food chain and get a stronger one. Having a marginal power supply for a rig more often causes instability, reboots under load, bsods. As long as your power supply doesn't blow up then it shouldn't cause damage to other components of your rig....As long as said power supply keeps voltages within tolerance of course.
On a side note I did seem to cause some MB damage on my overclocking adventure also. My MB will not shut down currently. It'll power all the way down for about 10-15 seconds then boots back up. I tried everything like you and figure it's gotta be the MB. Most of time this is blamed on Windows settings, bios settings. I'm gonna live with it as sleep works for me 100% everytime. Figure when Ivy Bridge comes out I'll pick up a combo at microcenter and deal with my MB at that time.