Well said Ian! I've just voted for twins, and 250 four stroke. The present bikes are far too fast for Newcomers to learn on, although surprisingly not much evidence exists that Newcomers are having accidents on the fast bikes. However, I can assure you that in my opinion they would REALLY enjoy learning the TT course on slower machinery.
The machinery today is extremely impressive........but boring.
Isn't it amazing how excited we all used to be at the sight of an overseas multi cylinder bike being on the TT course, and now we can't move for them?!!