Those are great clocks I can't wait to see what it hits on the LN2 BIOS with +93mv. Do tell after trying
No lock-ups happen because of the power limit, only throttling occurs (you'll see the core down-clock itself during the run). It has to be a crash caused from instability, which, judging from 1382mhz on the non-LN2 BIOS, it would seem pretty likely.
Heaven almost always crashes before 3dMark11, so if you do Heaven at 1372mhz then you could probably do close to 1390mhz in 3dMark11, and that's superbly high for the non-LN2 BIOS, so that's probably why you're crashing. Looking forward to your results on the LN2 BIOS
Also, I had the voltage up to +143mv when running 1460mhz and I was still only hitting ~110% Power %, so either way you don't have to worry about hitting the ceiling with that, but raising the Power % slider does seem to help stability for some one way or another.