I ran a Feigao 380XL in a Revo trannied E-maxx on 14 cells for a season of unlimited monster class racing. It didn't burn. Gave nice, smooth power which was easily a match for the nitro trucks. Used to wheely when it hit 2nd too.
You can get away with smaller motors in large trucks, you've just got to have allowances for it, like the two speed.
So long as allowances are made, and head is screwed on, smaller motors can be used with much success. I'd still rather have a bigger, lower kv motor though on higher voltages, buts its all good...