Hard to say. The Mavic uses cartridge bearings. Don't know about the XTR... Probably cones.
Typically Shimano hubs are standard cones with kinda crapy seals. Perhaps the XTR has better seals being an ATB hub.
I've heard that the industrial style cartridge bearings tend to have more resistance, at least from the seals, than do the cup-cone bearings.
Also note the cup/cone bearings can be adjusted to run "loose" because "you" must adjust them. The cartridge bearings typically are not adjustable... Actually care must be taken *NOT* to apply too much side pressure or the bearings will bind in the races. This is usually accomplished by the bearings being "pressed' into the hub and a spacer applied to each side of the inner race to help equalize the forices on the races to keep them in alignment.
My tandem's aerospoke wheels also seem to have higher drag esp at lower rpms in the "free rotating" position.
Not sure if there are any answers here except that the world is going to cartridge bearings because they are easier to service (because they are not serviceable)... Um I mean they are easy to service because you don't have to find threaded cones or worry about external seals and such... I had to replace a bad bearing in a brand new set of wheels recently and unlike cones, I could simply order the bearing by part number from an industrial bearing warehouse for $9. Nice that the parts are standard and not so bike specific now.
The price we pay for compatability with other industries?