i have a zalman 7000a with as5, the fan is turned down to the lowest speed using the fanmate. and with 1.79v going through my barton 2500+ mobile, my idle temp is 50 deg. my case fan is turned down rediculously low too, so i don't have great airflow...
if you're running default voltage, then it seems like you've done something wrong because it shouldn't be that hot unless you are running no case fans. that being said, others have stated that 50 deg won't break it, and they're likely right... but it might be worth figuring out why you're stuck at 50 on default speeds.
what exactly were you using to read the 'motherboard stats' -- try motherboard monitor 5 if you aren't using it already. the readings might be wrong, or maybe you put too much as5, or the bottom of your 7000 is uneven. those are my guesses.