I honestly deliberate between SG3 and SG4, but I believe that SG3 would be better for this game. In my opinion, SG5 is a bad idea, and I think that it even shouldn't be taken as consideration.
About SGV, I believe it should be a room-tag for people who want to use it in Duel rooms, train their aim and improve their skills, etc. It shouldn't be the default shotgun spread tho.