because those numbers are great over clockers. well specifically, 3939B078, you can overclock this one on stock air cooling all the way to 4gh'z and lowering the voltage.
I just got my I7 920 whit bach no: 3939B078.
It overclocks!!!!
I got mine to 4300 MHz, on air(Noctua). A friend got his (I7 920 batch AXXXX)3939 to over 4400 MHz with water cooling. I havnt had time to tested it more than 2 hours with Prime, but its seems rocksteady.
My cpu got 78 degree celsius on prime, but i think with some twicking i will cool it down
My i7 can run Prime95 fine at stock speeds with .95v
...I can't OC at all cuz I haven't found the right settings for my RAM though...
Lol, well. Funny story is that I never tried under volting untill I got to 4.1 GHZ and figured it was stable, so I'd start driving it down from there. I'd hate to bring it all back to stock and try it though. But at least the profile is saved, so I may.