CPU redlines at around 70�C (Intel Q9300 from about 2-3 years back)
Sitting in windows at standard clock it hovers around 55�C on a 30�C day.
Under 100% load it gets to about 60�C.
Overclocked from 2.4Ghz to 3.1Ghz average temp raises about 7�C
On a 40�C+ day I don't turn my computer on.
My PC is in a detached "unit" or as we call it a "granny flat"... I think Americans might refer to it as an "office"... anyway there is no aircon out here. Last time we had a 42�C day it hit 54�C in this room. PC was still running but CPU was dead on 70�C which is where transistors start to screw up.
I guess with 2xGTX280 GPU's and 6 HDDs in this case... it like a 3-bar element heater running on full. The stock CPU fan that came with the thing was so crap, my system would overheat and bluescreen if I did anything beyond sitting at the desktop. If I take the video cards out and put in something milder (like a 9800GT or something) I notice about a 15�C drop in ambient temperature.
This thing is on the edge. :/