I come at it from another angle.
IMO, if I pay for a 50 grade I want it to remain a 50 grade for the full duration of the service interval. Engine and transmission rebuilds aren't cheap, and I don't need any more power because It's nearly impossible for me to use all the power I've got.
A thicker oil helps to keep the engine running quiet. A quiet engine is a happy engine
Besides it would be impossible to measure any benefit through lap times, of having 2-3 extra hp from using a thinner oil on most tracks.
Then there's the approach that Bonaventure has, which factors in some oil shearing whilst in service.
He fully accepts the possibility of starting out with a 50 grade only to have it shear down to a 40 grade at the end of the service interval.
It's sort of a bet each way.
He won't entertain the notion of having a 30 grade oil in his machine at all.