My advice would be to avoid buying a "generalist" gun that forces you to make compromises.  If you are like most people, you will simply end up replacing that "compromise" gun down the road with something that really fits what you need.  I have several guns in my safe that were purchased to go between upland and waterfowl and probably could have saved myself some money by just holding off and buying two specialty guns. 

My end result: Benelli SBEII for waterfowl and a Franchi AL48 20g for upland. SBE adjusted to "fit" the same as the Franchi.

The SBE is not a heavy shotgun per se and I have carried it in the Upland field, especially in nasty weather because it is so durable.  I would not want to carry it for 5 days on an early season upland hunt. However, the 20g is at least a full pound lighter.  You can get the 1oz load of 6's at 1400fps - kills long tailed birds at any angle in my reasonable shooting range.  Pick what you really want your upland gun to be or what you really want your waterfowl gun to be and make the investment in what you want.   

3.5" loads make some difference at distance when shooting steel.  They also pack more punch with late season geese (using steel).  With heavy shot or similar, 3" loads are just fine, better than 3.5 steel.  I dont take shots at geese that are long enough for a 3.5 heavy shot to make a big difference.  Heavy shot is more expensive but I seem to be able to pick up a bunch about this time of year on clearence for less than half price.