anthony, here's my $.02.
i hunted for 15 years with a 20 guage pump, 3" steel #2 and did just fine because i knew how far i could shoot reliably, which wasn't far (35 yards was about it). then, because new guns are just too fun not to try, i went to a different extreme and bought my second-ever shotgun, a beretta o/u chambered for 3.5". i also started using hevi-shot #2. my findings were several. one is that what you shoot good with, you shoot good with, whether it's a pea-shooter or a cannon. but there's absolutely no question that 3.5" tungsten shells will double your range. for me, that's useful and not. i just don't like shooting non-decoying, close-in ducks. i was raised hunting timber and little river sloughs, so we never pass-shot birds, and i still won't do it. still, if your buddy misses twice or nicks a bird, you can reliably, with practice, drop the bird dead at an honest 60 yards. and i mean dead-dead. also, with big ducks, there's NO comparison between steel and the polymers regarding kill-rate: steel sails a lot of birds; polymers drop them dead, no matter the distance.
now, the downside. one is price. i can't afford hevi any more, period. two is kick. a 3.5" shell with tungsten shot in a light-ish gun will absolutely hurt you after a few days of shooting. the last year i hunted a lot, i got to where i had to stop because my cheek was so swollen. third, that stuff REALLY tears birds up. forget whole, roasted birds--you have to breast them and cut the hematomas out.
so for me, i've kind of reached a middle road. for little ducks early (teal, gadwalls, young birds) i shoot kent faststeel in #2 or BB (remember: steel has less energy than lead, so bigger is actually smaller). later on,when the birds are big and really plumed, i use the fancy stuff, but in 3" or even 2.75", and in smaller sizes like #3 or #4. this year i'm trying kent tungsten matrix, which is supposedly easier on barrels, and is definitely easier on the pocketbook.