I think the upper limit of cpu temp on a q6600 is really only reached when you feel uncomfortable with it or it won't run stable. OCCT will definately generate lots of heat and stress the system very well. A couple things to consider, case airflow and placement. I like that sunbeam case and I have a similar one but even the best case designs and fan setups aren't going to help if the case is jammed in a cubby, wedged in a corner, or near a heat source. The ambient temp of course is always very relevant with air cooling. The one test I looked at with that coolermaster sink was at anandtech. The results using the stock fan were very middle of the road and that looks like what you're witnessing first hand. Once they strapped on dual fans the difference was impressive.
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