I think maybe the air cooling just isn't as effective as water cooling for the 2.7Ghz, hence the fans need to spin up to keep it cool.

Btw. my 2.5 also sits at +-160f ( 71c ) all the time.

The difference is no matter what I throw at it it doesn't rise or the fans spin up. I have left MDW's demos on loop for hours and the CPU is pegged at 100% and it doesn't rise.