No size difference. 457 has an alloy frame, so it weighs substantially less, which makes it easier to carry and harder to shoot alot. The pistols take the same mags. The 4516 is too heavy in relation to its size and if I were going to have an all-steel pistols, I would prefer the 4566 instead. The best choice for carry is probably the 4563, the alloy framed version of the 4566.