I know a pilot (that will remain nameless because he's in the US ) that clocked his hotspot at 278MPH with a ~27lb turbine at full bore. It was done safely in a wide open area with no one around... In his words, he "lived to tell about it" and doesn't recommend anyone else try it.

Incidentally, this proves its good practice to bolt the verticals onto the hotspot fuse because there was no hint of the usual flutter when approaching those speeds, even with balsa sheeted fins.

Kelly