Yeah, as with Nathn, I thought that the OS freeze was actually a crash. Takes me a little longer just as I have 8gb to run through.
As for HWMonitor, as long as you can still monitor the max temps you'll be alright.
I don't think Intel Burn Test itself really pays attention to the temps; if it gets too hot, you'll probably just BSOD, or your CPU will throttle, which will likely end with IBT failing. The CPU seems relatively good at saving itself mind you; never actually had a BSOD using IBT.