At least for UAVA there is really no easy to do this. You need someone who is very experienced in using a certain gun be able to spot certain differences from pre-nerf/buff to post patch. And getting several people to do it is a very tough thing to accomplish. At the very least, look up some video reviews before buying/deciding on a specific gun. They will at the very least do a crouch/standing and burst/tap demonstrations. Some will try to to range tests. Few (or none) would go very far to comparing mods.