Proshots,
If you look around your local skeet club you will probably see that many of the shooters have gone to 28" and even 30" barrels. The shorter barrels will not handicap you ballistically as modern shotshells use up most of the powders energy by the time it gets about 20" down the barrel. There is a slight increase of velocity from longer barrels but it is negligable.
Pick the gun that feels best and shoots best for you. If you do much upland and walk quite a bit, you might want a little lighter gun but the little added weight of the longer barrel will make the 28" gun a better shooter for you.
Chuck Graber