Also remember, there's a big difference between a modern R/D longbow and a Hill style. There's really three classes of laminated trad bows IMO instead of two.
As for power/efficiency, I read one time where a guy did a testing that. He used one recurve and one longbow, so I'm not sure how well it applies across the board, but it was interesting nonetheless. He used a recurve and longbow, not sure the model/design, of the same draw weight and chronoed them with a variety of arrow weights. With the lighter arrows, the recurve was quite a bit faster, but as he increased arrow weight, the gap narrowed. When he got up around 15 gpp or so, I believe the longbow actually caught up and maybe even passed the recurve. Like I said, I don't know how scientific the test was, but it seemed to indicate that it's not so much that recurves are faster, but that different designs need different arrow weights to maximize efficiency.