Dunno but the items I bought from B&C express above were fine for 2 teeth up on the rear.
Incidently, at 100mph my revs are exactly 5500rpm with 39T rear sprocket. See what your revs are at 100mph with 37T rear and I bet they will be only a few hundred lower at most. I can still pull 140mph (althought that's maxed out).
** Note: all the above figures were carried out in a controlled off-road environment by professional riders
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