I've got a VFC gas shotgun with the 30rd shells - same system as Marui, Cyma et al. On 3rd spread, it's a decent distance - I've never measured it but it's not that much worse than a typical AEG. On 6rd it probably loses 5-10m of range but obviously a bigger spread. I've played outdoors with it a couple of times and not felt completely outgunned.
I think it also depends a little on the site you're playing at. If it's got wide open spaces, hundreds of people and everyone has a hicap then it would probably be a bit pants. Most sites I play at these days are built up/dense woodland and the games are semi-only with most people running midcaps. In those, if you pick your shots it's no disadvantage at all and makes for a very rewarding game. You do have to be on it with gassing up the little tank though.