If you're a fly weight a decent RS125 would be awesome, 71kg and 45bhp, if you've got the skills you'll destroy the fast group.

Comparing laps the 125 race class and 400cc road class lap times (which as we know the 250 road bikes struggle to match) are very similar at club level - Billy, sub 1.17 Donington national circuit??
The British 125GP (the BSB support race) guys are quicker than either the superstock cup or r6 cup.

I made the mistake once of trying to chase an RS125 through the bus stop at Mallory, bad move, the grip would have come off before the bike turned that fast.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread