But the argument is that loaded friction is different than unloaded (I'm a sceptic).
With a larger ID bearing the friction of the seal, grease, and bearings acts over a greater lever. If everything is otherwise the same, the drag of larger ID bearings will be greater.
For what is used on road bikes the difference in OD is never going to be more than a couple of mm which, all else being kept equal, should not make much of a difference unless we're talking miliwatt range.
All of these industrial bearings are originally engineered for high loads/high revs., they don't care about contacting seals as these don't bother them for too long. These seals are broken in fast at such high revs. after which they no longer cause drag.
Bicycle bearings run at at low revs and low loads and should be designed accordingly. They are not. A Few exceptions notwithstanding.
Even the best available bearings are still using contacting seals, are still lubricated with a lube that's not drag free.
Anno 2013 one would have hoped for better and moreover that this would have been implemented throughout the entire bike.
Sadly, it is not. Worse still, some aereas benefit from fine tech whilst others are completely ignored essentialy cancelling out the benefit of new tech in first place..... Go figure...
A couple examples:
Most pedals run on an industrial bearing and a bushing. How do you lube this correctly so it does run drag free without sacrificing the bushing? You can't.
What then is the point of running a crank on oil lubed high grade ceramic bearings?
Same for the freewheel. Coasting or not this is bound to be the achilles heel and mother of fricton. Again a combination of a bushing (of little impact once it's loaded) and a set (or at least one) of bearings that are not up to speed.
Again, little point in running top ceramic bearings in that rear hub when all is going to be dragged down by a set of steel bearings that, once again, are going to take like forever to run in anyhow?
How about chains? Tyres?
All the tech is there but no one really uses it to the full. Pity...