250g limit? Hmm.
I recently built a very light FPV quad which uses 5" props and weighs 163g without the battery, if I pick the right weight battery it'll be under 250g total - and this thing goes like a rocket, a rudimentary test with an old 3 cell battery tells me it's going well over 60mph, I suspect it'll go 80mph or maybe faster with a new 4 cell battery but I'll need a radar gun to measure it...