It's only a wheelbase question.

TBA/SM have too long wheelbase for twisties, and if you arrive too close to the inside of a curve you're abliged to brake if you don't want to go out on the other side risking to go offroad or crash with a vehicle coming from the opposite.

To drive with a so long wheelbase you've to prepare curves and learn how to drive in a racing circuit for best time.

Arrive large to the curve and close the stearing just at the last moment to go tangent to the internal of the curve.
You'll be faster and will be able to stay closed to your friends.

With their shorter wheel base they can go faster on twisties, also if they're not good driver.

A good driver with a TBA/SM can go faster than a bad driver of a bonnie/thruxton.

That's why in Italy we don't like easy roads.
And if a road is too easy, in some kind of races we make artificially more difficult...

http://www.youtube.com/watch?v=ZMMwUeKQ3qg

Come to Italy, me and some friends of mine will teach you on our mountains.
If the bike's world championship is italian, there's a reason...