I'm interested in these answers too. My single is Rev E (shipped Aug 22) and came with 872 firmware. Which was odd because it would throttle almost immediately. I took the case off and got it stable with 832 firmware. Watching the temperature in CGminer (often cycles up & down), I've not seen it go above 48.2C so I figure that must be about the throttle-temp-trigger. However, if I load the 864 firmware and watch the temps, it appears that anything above 45C will trigger the throttle.
I should take the heatsink off and apply that Artic Cooling paste to see if that'll lower it any.
What is your ambient room temp? This seems to have a dramatic effect on speeds. Also, having an external fan pointing at the units helps a lot.
Several of mine shipped with firmwares that weren't remotely stable in my dwelling, not sure why BFL doesn't use a standard (lower) firmware.