I'm not saying it is, but I just re-read the instruction manual that came with my Quark. It says "over 4s a BEC is required". I didn't think I was that much of a stooge. I'll be running external BEC's from now on just to be safe.
I did have a super high torque digital steering servo in my E-Maxx when the Quark blew but I never gave it more than 4s.