I think the zed time nuke damage is also a LOT higher on the RPG. I've seen it kill scrakes that it hasn't even hit over a few seconds from full hp.
If you ever want to see specifics on damage and such, just check out the source code; if you have the sdk downloaded it should be in your killingfloor2/development/Src folder.
Useful things to look for:
-ClassName-Folder it's in-
-KFPawn_Human-KFGame- specifics on the player such as movespeed
-KFWeap_x-KFGameContent-weight and other things associated with a weapon
-KFProj_x-KFGameContent- arm distance of projectiles
-KFPawn_ZedX-KFGameContent- specifics of the zed (things it can do, damage it does, vulnerabilities and resistances it has, etc