The gun with the softest felt recoil, IMO is the Xtrema II, with the Browning Gold/Winchester SX2, and the 11-87 close behind.
I have used 3.5" shells, but really don't need them. 3" steel high velocity loads (around 1550 fps) will work great. I like 2's for ducks, BB or BBB for geese (but HV...