John, my own repeated rollability test data shows that the #566 Kadee Barber S2b truck rolls best with either the 1.020" or 1.025" Reboxx wheelsets (both in the lower acceptable range), with the 1.030" sets performing considerably less well (in the mid-poor range).
Of interest, rollability test data of the same truck with Kadee's own wheels, either with the traditional 0.110" tread, , OR the new 0.088" tread (same 1.020" axle lengths), shows that they roll just about as well as the Reboxx -almost exactly, in fact.
These are very fine trucks, whose weight incidentally adds considerably to overall car stability (and the need for less car weight). My only disappointment is that they do not roll better than they in fact do, regardless of wheel-set choice.
Denny S. Anspach MD