I am by no means an expert on this subject and there are many here that are but, I believe the problem is not in the voltage for the larger servos but the current draw required through the Rx to those servos. I don't believe the micro servos can handle the current draw and would burn up in short order. Many people flying 40% planes use two Rx so they can split up how many servos go through each one as their current draw is enormous. By using two they can split this in half and reduce the risk of losing a plane to a burned out Rx.