Does hub diameter or hub size have a notice able effect on the aerodynamic performance of a wheel set? If you were to change the rear hub on your hypothetical or real zipp 808 wheel set to a large diameter internal gear hub like a shimano alfine or a rohlhoff hub would there be a measure able aero dynamic effect?
There would be a measurable decrease in drag from removing external dérailleurs and gearing, however I would guess that the power loss through an internally geared hub would make such a setup slower rather than faster.

(I have no sources for this)