e-maxx user looking to go brushless need opinions

Ok I read over that thread but I still have a few questions. Whats the difference between the Feigao 540C XL Brushless Motors and Feigao/Nemesis/Wanderer "XL" Brushless Motors? I believe you were talking about the 540C motors. What kind of speed will I be looking at with your suggested motors? On the 9920 description it says 3Amp.BEC on/off function, what does that do?