I've seen mp5's out shoot m4's. real steel the round difference would put those two in separate classes, but remember we all shoot the same size ammo *less the 8 mm crowd* and we are all roughly around the same FPS *less the snipers*. So get something that is easy for you to use.
they both use a V2 mechbox, I think that ICS might be the split box... velocity arms is being gay and not letting me load the page again.
Really the "shell" of an airsoft gun has no bearing anymore on the actual use of the gun. Hell I have used a p90 and PPSH very effectively in the woods... the DSR is a little unwieldy in CQB granted lol.