Today I hooked up the ESCs to the real power supply (rather than the bench supply) and the motors fail to start - in fact the ESC will often reboot itself. What gives? Well, it looks like the instantaneous power requirements for starting a motor cannot be met by the BEC I chose. I tried adding some big capacitors to see if that would help with startup, but no luck. So back to the drawing board on supplying 12V. I'll try a 10A buck converter and see if that solves the problem.

Update 1/30/16

So I checked the inrush current of the motors (the instantaneous current required when the motor starts moving) and it appears to be 3.5A. Obviously a bit too close to the 4A BEC limit.