What C.W. just said.
It is difficult to assess the impact of the fast angle of the wheels themselves, since I don't believe anyone has ever produced a wheelset with the 90 degree (flat) tread that has the wheels rigidly attached to needlepoint axles.
The only exception may be some wheelsets with smaller (closer to scale) flanges produced in the 1950s era by Walthers and Auel, among others, and intended primarily for 2-rail use.
You would need to compare rigid axle designs for both tread types for the results of a rolling comparison to be meaningful.
Jim
