Not sure about the temps coz I never care about battery being hot as battery temperature really has nothing to do with CPU temperature. (battery gets just as hot even at stock clock speed when phone is constantly under load) I run mine at 1.1GHz constant and have no issues playing an xvid video for an hour straight. I do this nearly everyday on the way to work and on the way back home.

But yeah, results will vary depending on the N900. Guess I have a fairly good sample.