I don't quite get your case setup... The power supply blows air INTO the case? It doesn't suck air IN and blow it OUT the back of the case??

Your "pretty large fan" above the graphics card exhausts? (blows OUT the back of the case?)

I build Home Theater Computers so I'm fairly obsesive about cooling, airflow, and noise. That's why I use fanless graphics cards. I've learned that "just adding fans" doesn't always equal better cooling.

Your case needs to have a good airflow scheme in order to keep everything cool. In a "tower" case, that means it needs to pull cool air in (hopefully from or near the bottom front), make it flow PAST the heat producing components, and get the warm air OUT of the case (usually at the back as high as possible - thats why most power supplies are mounted at the top rear of the case AND they usually EXHAUST air (pull air through the PSU to cool it and blow it out the back to get it OUT of both the case and the PSU...)). If you have an HTPC style case it gets a little trickier.

Oh, air coming out of the PSU WILL be WARM - generally you don't use that air to cool other things off...

edit: forgot this: Unless you've lost all feeling in your fingers, if the temp of the heatsink is much above 125-130F (low 50's C) - there's NO WAY you could keep your finger on it for 5 seconds without getting burned. The heatsink will be cooler than the GPU core, but if the core was running 80C the heatsink would probably be 70C - 70C is about 160 degrees F. 160 degrees F would burn your finger in a second or two... Slowdown temp for the GPU core is 125C (260F), which would burn you just looking at it ;-)

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Running both 10.5.8 and 10.6.4 on my stinking AMD/ATi machine...