FYI, for anyone having issues booting after updating to the new 4.1 bios on their p67 boards, if you also have a 6950 2 gb flashed to a 6970.
Symptom: After updating to 4.1 motherboard bios, system would not complete post (only partial post where usb devices were powered on).
Resolution: Set 6950 video card bios to default (video dual bios switch to position #2).
For some reason the new 4.1 bios doesn't like the 6970 bios on a 6950 card. The old motherboard bios worked fine.
Also, just to confirm what another poster has seen regarding the 4.1 bios and sandy bridge overclocking, it seems a lot more difficult to get a 4.5 ghz oc now. I was able to get a stable 4.5 ghz by just changing the multiplier and cpu core limits in previous bios but not with the 4.1 bios.
Basically, I would stay away from 4.1 unless you have an ivy bridge cpu.