When it comes down to it, if the oil supply is sufficient there should never be any bearing contact, should always be floating in oil, so no wear ever.

Providing your oil sys is good enough...

Bearings, engine or turbo, primarily wear due to no reason barring inadequate oil supply.

"technicly" BB should spin freer, but the amount they do is so tiny its not one you can feel. the reason BB turbos spin up quicker is far more modern wheels/housings that are genrally fitted at same time.

seen a few tests, MikeR did one with a T4 actually, same spec just swapped from BB to normal core, no noticable difference