I wonder if the irregular power curve up in the revs is a result of reed valve 'flutter' on the 6100.
A change in reed material or thickness might change the curve.
I always wanted to see how a different set of reeds would affect the 6100. I suspect the factory may have found a particularly strong running set of reeds, but the reeds could have been too fragile for commercial sales and it would reflect poorly on the 6100s reliability.
If I ever get one of those puppies, I'd go with a bigger carb and thinner reeds with probably a lower reed stop.
EDIT: Was the 'limiter jet' in the carburetor's low speed circuit enlarged?