How hot is too hot

Hi everyone,

I'm trying to decide what's the best tradeoff between performance and noise for my home computer. My cpu is an Athlon X2 3800. Using the default core voltage, my cpu overclocks to 2500MHz, and is completely stable. The problem is that my rig is setup to be very quiet, using slow spinning fans. The cpu is cooled with a Zalman 7000cu (or something like that) with a 92mm fan running at ~1400RPM's.

With the cpu@2500MHz, and idle, the cpu temperatures are about 43-45C, and my system is very quiet. However, I have need to run some very cpu intensive programs, and when I have both core running at 100%, the cpu temperature rises to ~60C, sometimes a little more if the room is hot. If I increase the fan RPM to around 2000, this temperature is more like 57C. However, this also generates a lot more noise.

Does anyone know how the safe upper limit for the cpu temperature?

Thansk