Kelly, there's nothing wrong with a guy doing 278 if he wants to. AMA can't say boo about it. They just won't cover him for insurance, that's all!
As long as he is somewhere where he cannot hit somebody, it should not be an issue for anyone. That's what dry lake beds and such are for.
If he did 278 with a draggy thing like a hotspot, you can imagine what the speed would be with the same power in a cleaner airframe like a Bandit or Razor or whatever. 300, I would guess that somebody has been there already.

Fastest RC flyer I know? Bob Parks, did over 400 with a drone, dropped from a balloon. Another glider!