Trevor,
maybe you weren't around in the 60's, but we had several failures with multigrade oil. The oil pressure would collapse - and stay that way until it was replaced with fresh. The ballrace theory was from the experts at the time. Don't understand the 'space between teeth on a gear' - that's dependent on pitch, but if space between gears in mesh was meant - well, that depends on loading and oil film (if any).
Just to add: I have 4 bikes on monograde (3 on Castrol R) and 2 on multigrade - the Firestorm my GF Vee twin. My boat engines and all road-going vehicles are multigrade. I reckoned by the turn of the last century the bugs had been removed from the early iterations of multigrade. Nontheless, I remain of the opinion that the best oil for an engine is what it was designed around.