I have experienced brown outs with Spektrum receivers and Savox servos. They were all the sport servos, like the 210 and 310. The micro receivers and higher end ones dont seem to have a problem. I think I did have a problem with the AVC receivers, but dont quote me on that one.

All my 1/8th scale, my wheeler, my 1/8th crawler (4WS) and one of my 4WD SCTs use Savox servos with Spektrum receivers with zero issues. They all have Hobbywing ESCs in them. Another problem I know of is with Castle ESCs, they dont get along with Spektrum very well, I couldn't imagine throwing a Savox in the mix would be a good idea. In that case I would definitely use a good BEC.