The fans on the heatsinks have a 4 pin connector, so they definitely have the ability to vary the speed. I have no idea if they actually do or not. It seems as though the CPU coolers are complete overkill though. I tried it out with removing all the fans, and just put one external fan blowing at the system with the case open and the temps were 40 degrees or less, but the hashrate in that format was around 450-490.

after more than an hour now, the rear 2 modules are staying steady at 70 degrees and the front ones are still at 60.  (+/- 2 degrees)

The hashrate reported by the device is now 558, and hashrate at the pool is reporting 549. I'm extremely happy right now  

*edit* this is using the .98.1 firmware. I tested the exact same setup with the .98 firmware and I initially saw good results but within a few hours it was back down to 460 or so. it's only been a couple hours with the new firmware so the jury is still out on this one. Will have to wait and see if it can maintain these speeds, but it's looking solid so far.

Also, as a side note. If the optimal temperature is actually 70, then I would like to push more voltage and clockspeed to this thing until you reach the point where you are struggling to keep it under say 75 or so... restricting the airflow to intentionally increase the temperature of computer hardware is really twisting my stomach in knots.