The main diference is in the Data-bus contacts, used to transmit aperture information to 2000-series bodies. They are present in the "E" type tube, not in the old 55 mm or 56 mm non-E tubes.
The remaining difference simply is the 1 mm difference in length. How much this affects object size covered depends on what lens you put on it/what percentage of the total extension (more tubes? Built-in lens extension?) this 1 mm difference would be.
But it will not be a lot.
Here are two formulae to play with:
1) Magnification = Total Extension / Focal length
2) Object size covered = Magnification * 56.5 mm
Image quality depends on what lens you put on the tube.
Exposure compendation too depends on total extension used and the focal length of the lens in use. Even when using the shortest focal length lens available for Hasselblad, i.e. the 40 mm Distagon, the difference in compensation needed between using a 55 mm tube and using a 56 mm tube will not be more than approx 0.02 stop, in other words nothing. Even less when using longer lenses. ;-)
Try to get a copy of the older Hasselblad info brochure on "Close Up Photography". It has nomographs in the back covering, as I recall, the 10, 21 and 55 tunes, in adddition to the bellows, for the 80, 100, 120, 135 and 150 (250?). Shows exposure factor, magnification, size of field of view.