no back to back comparesons but my 421 cub had small bore rdzs on it, switched to bb shearers, bike seemed to pull a bigger gear easier but would not rev out as far as the sb's would...
I sold the 421 to my brother who is trying to buy a set of sb shearers for it right now, so this spring we will be able to back to back track test it with both sets.
so far to date with the bb shearers the bike went 4.08 in 300ft.
more to come stay tuned