Unless you'll be goose hunting a lot, I'd reccomend skipping the 3 1/2" guns. I have 2- 3 1/2s. One first year 835, and one Franchi 912. I rarely use 3 1/2"s, 3" will kill them just as dead. For steel shot, speed kills. And across the board, each manufacturer's 3" shells outperform their 3 1/2" shells.
If you have to have 3 1/2" chamber capacity, here are some observations I've made over the last 15 years of 3 1/2" guns...
One of my friends has a Rem. 11-87, 3 1/2" gun. His gun will not function with 3 1/4dr.-1 1/4oz., heavy dove loads. It took some of my handloads, ~3 1/2dr. and 1 3/8oz. of shot, to get his gun to function. Now all he buys is high brass.
Several friends own Benelli SBEs. Not a one of them can function with 1oz. or standard 1 1/8 oz. loads. They have to buy highbrass 1 1/8 oz loads to function reliably. When they were new, one would barely function (sometimes) with 1 1/4oz heavy dove loads. The other wouldn't even reliably function with those.
My Franchi will reliably function with a standard load and 7/8 oz of lead. I loaded some ultra-light 7/8oz shells for the high volume days, it's hit or miss with those. Sometimes they'll fully eject. Sometimes they won't. The Rem. and the SBEs won't come close to functioning with the variety of loads the Franchi will. (Just comparing my 912 to friend's 11-87 and SBEs, side-by-side comparison.) Yes you have the valve to switch. But it will function (just more stress on the action) in the light load position, with any load. If it's set-up for heavy loads, it won't function with anything lighter than 1 1/8oz.
If you want complete reliability (with all possible loads) out of a 3 1/2" gun, buy a pump. 835, Nova, 870, BPS. It really doesn't matter which one, it's all a matter of choice.
If you buy a pump, the first time you touch off a 3 1/2" turkey load (2 1/4oz of lead shot), you'll be asking yourself, "Why did I spend the extra money on a 3 1/2" gun:banghead::banghead::banghead:?" Steel's not so bad, but you'll know when you fire one in lead.
Happy hunting (gun and fowl)
Wyman