Does anybody use an aftermarket GPU cooler with this board? How have you plugged the cooler in?

I have an Akasa Vortexx Neo on my new 4850 which has a three-pin connector on it. Therefore I have to plug it in either into the PSU directly or to a P5W fan header.

I have it plugged into the 'CHA_1' connector at the moment, I've also tried PWR_2. Basically, 3d intensive stuff seems to crash after a few minutes when graphically intensive games are run. Speedfan doesn't seem to think the fan on the cooler is spinning up much, and judging by the sound this seems to be correct.

How can I get the cooler to spin up properly, as when I run GPU benchmarks, the temp just seems to go up and up