The fans inside the Mac Pro are almost at idle speed.
Hmm, well it's hard to say from sitting here in Japan but this really doesn't sound good to me.
- Mac's fans almost idle (500 ~ 900 RPM),
- The Card is at full draw according to the UPS (approximately),
- The Card's fan doesn't rev to the same as it does in Win7, and stays very quiet comparatively - give similar loads,
I suggest downloading Mac Unigine-Heaven-3.0 or Mac Furmark, removing your case's side panel, and letting it run through the demo for 15 to 30min and see how hot the card is getting to the touch. It should get hot enough to be painful when you momentary touch it (like a large pot of boiling water 30s after you take it off the stove) but not hot enough to melt stuff like wires and so on.
I think you should be able to tell by common sense. One will seem like gosh that's very hot and the other will be like holy cow that might start a fire.
If it's the later you should hurry up and figure out how to solve it. The Mac's PCI fans under SMCFanControl can do quite a lot. Maybe rex those to 1300 or 1400 and don't work the card hard till you figure it out.
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EDIT:
Sorry, I read this later:
Update: After doing some testing with Unigine Valley, it does appear that the GPU fan kicks in immediately.
Oh, OK, you're fine then...
Now the question is why do the fans not kick in when playing games for hours at a time?
It's just not heating it up is all. AFAIK it all works from thermostatic readings. It doesn't care about load or rates or anything... just temperature. So if the fans rev up in one circumstance then this shows the fans and sensors are working and you can go back to not worrying - even marveling at how much quieter OS X is than Windoze...
BTW, I play some games that look awfully heavy yet the 8800GT's fans barely increase at all... QuakeLive at 1920x1080 with everything set to high or ultra high, and all post processing turned up to max. CPUs system wide are less than 20% (usually around 10%), and the 8800XT's fans are not audible over my SMCFanControl setting of 1300. The card draws 90 to 95% of it's max power specification according to "Hardware Monitor". Furmark on the other hand revs the GPU's fans to max - or ver near max...
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