The other cause is the miner needs more voltage to run at that mhz. If that is the case I can make a bminer at 8.9v or even try at 8.7volts. (I don't think 8.7volts is going workout to well though and cause lots of HW errors but I can build it)
I have found that at 750MHz the miner works best with 9.4 Volts. 8.8 is probably too low.