IMHO the 3.5" is great for shootng steel shot at geese, and hevi shot at turkeys and varmints. For anything else 2.75 and 3" is all you need. I love my Mossy 835, but it is my least used shotgun. If you want it, buy it, but the weight, and longer throw of the slide really kills it as an upland gun.
BTW 3.5" shells give brutal recoil, especially the Hevishot ones, be prepared, be sure to shoot several boxes at the range before you use the gun for serious work.