Personally, I think (without thinking too much) that the 900SS would be good.
However, is it enough of a jump? 20bhp over a 620?
Maybe it would need the attraction of slicks/wets & warmers?
I suppose the 748 has about 90-95bhp? and is a 'proper' race bike.
I think the 600DD series is 95% spot on at it's first attempt.
Splitting the 583, 675 & 620 up could be awkward, as a 583 class and a 620 class would be better (within one race), but what happens to the 675 boys? I think it would be too much to have 3 classes within one.
A single tyre with no wets/warmers for the 600's?
Otherwise you could have entry DD and expert(?) DD being too similar.
I dunno, just waffling on really
