[hemiblas]

This is just my opinion, but the only 2 times I fried speed controllers is when I tried to do something similar to this. I overgeared and overvolted a couple of setups and I let the magic smoke out after running them for several minutes. I think this setup stressed the speed controller and caused it to fail. I dont think it was your fault though. With specs like "more than you can handle", it is implied that you can do just about anything and the controller should be able to take it. I have also read that the more efficient a motor is, the higher the instantaneous peaks will be.