Super-Dave,
I have a Remington SP-10 and a couple of 12ga. shotguns that will shoot 3-1/2" shells. I have a Winchester SX2 and a Browning Auto Magnum that shoots 3-1/2" 12ga. shells. If I shoot the Browning with 3-1/2" shells, it feels about the same as the SP-10ga. But the Winchester SX2 will kick like a mule with the 3-1/2" shells compared to the SP-10.
Shooting the SP-10 and the 3-1/2" 12ga.`s are not too bad as long as I don`t try to shoot trap or skeet with them.