64c is fine for 3.2ghz
i've got the same rig as you, and 4ghz i idle at 40-45c and max out 80-82c
I've been running this setup for over a year and it's perfectly fine.
You always want lower temps, but the i7's do run hot.
Like Sayso said, these are bench tests, in normal conditions, the highest temps i've seen whilst running a game or encoding a video is around 70-75c. And that was during the summer, so go ahead and squeeze more out of the 920.
Just don't too nuts on the volts