Then I'm screwed, no other words for it. Will have to plug E8600 into DFI X48 to see which one of the two it is (board or cpu).

Edit : which bios did you use ?

0725, best there is afaik (though an unofficial bios)

Last Q: VTT for E8500 @ 500FSB ? Did you have to use GTL-ref ? Any other tweaks ?

500FSB was completely untweaked: I just set the lowest voltages and boot 500x8 (vcore was raised though)

Oh well, CPU can be RMA'd so it seems so no harm done.

I'm totally baffled honestly. I can make 4Ghz with 400x10, 1.375V (not very good, but at least I made it ;) ). ANything over 425FSB is a "C1" though, and I honestly don't know how to fix that.

Only 1 question : is this the board or the CPU ? What do you think ? I can RMA the cpu, but not much use if it's the board. Another question : could it be the ram ? Which ram did you use (currently on Corsair dominator) ?

I honestly wouldn't RMA a cpu if it wouldn't hit the overclock you'd hoped for.

The cpu is eligible for RMA, as it is defective (the stuck sensor bug is a known issue for Intel, they'll replace it for sure).

But to answer your statement : why should I keep it when I can't OC it ? So what should I use it for : heating the room ? I bought it specifically to OC, so if it doesn't meet it's requirements, it has to go.

From the looks of it, it seems that you either have the worst dfi P45 or the worst E8600. 4G with 1.375v is really weak, so I'm leaning towards the E8600 being crap, although I can't figure out why that would affect the FSB ocability so badly.

ow man that 's a sucky E8600... mine did 4.5Ghz 1.36 stable 24/7 and even benched under water at 5Ghz ( only superpi 1mb and AM3 )

The voltage requirement for 3.8ghz is not a good sign at all mate, you got another s775 board to test it on ? otherwise you can get my UD3P with DDR3if you want (if I can get an X58 next week) : though that board is really a challenge to get going unlike it's DDR2 brother that just flies out of the box