It's interesting to read him say that it's a body double, if it is it's a very good match for Mark both facially and in terms of body language (It would also mean I would have to apologise to Vbangle who insists it's not Mark).

The footage in the meditation chamber looked like a composite to me as the helmet looks really glossy (as in the ROTJ style).

Does this mean that originally Vader was to address the Emperor from his booth in ESB (explaining his bow) and the hologram was later moved to outside the booth where he could kneel with more style?