You're sorta comparing apples and oranges. If by deposition efficiency you mean weight of weld metal per inch of filler material (a popular method with FC's or stick) it is meaningless to compare .045 to .052 IMO. But, overall MC will see slightly less deposition efficiency, due to space in between powder particles, increased alloy loss and oxidation due to increased arc density, than solid, and greater deposition rate with MC's per any given current setting for sorta the same reasons.