You're running a model 6 cpu (palomino, the voltage is 1.75 voltage) XP1600 doesn't exist in a model 8 cpu...(thoroughbred)
I've had similar problems with my XP1800+ and currently with my 2100+... but alas I have found the actual source to the problem to be the heat sink, combined with the shape of my cabinet.
There just isn't enough airflow to cool the cpu, so the hot air goes in cycles around the heat sink, and eventually I reached temps as high as 78 c's on my 2100c... still stable... but it sure made me throttle the ******* down to a lower frequency.
Right now I have a fanduct and some parts en-route, along with Arctic Silver 3, and by the end of this month the baby should hit <50..
So get with it matey, more cold air, stick with your AS3.. and you'll go low as well.. and don't panic... it'll survive it The palominos are known to get pretty hot, whilst the thoroughbreds are somewhat cooler..