How are you checking the temperature? Two things to consider - sometimes applications running on Windows can get incorrect readouts, and I'm fairly sure that CPU usage is a lot higher than it ought to be while in the BIOS settings, so don't spend much time monitoring the readings there.
Presumably the problem isn't this or you would know by now, but it may be worth mentioning anyway - I once built an s1366 setup, and I thought I had the HSF installed correctly, it certainly looked ok (felt ok too, IIRC, but the memory is vague), but within about a minute of it being switched on, it went into thermal shutdown. The s1156 HSF installation is near-enough identical, so I wonder whether you could have not-quite-correctly installed the HSF, yet not screwed it up enough to cause thermal shutdown. I just thought I would mention it. I always have a hell of a time with anything Intel post Prescott wrt HSF installation.
I've built an i7-870 based setup and an i7-920 setup. IIRC the temperatures weren't as high as that on idle.