It used to be a hands down difference. When I started hunting we always packed out the 12 gauges with 2-3/4" shells and had a 10 in the blind with 3-1/2 copper plated lead mag bb's for geese. You could kill a goose out to 100 yards or so it seemed. Now with the new 3-1/2" 12 gauge shells, you don't see a ton of difference. It has definitely leveled the playing field. But, the 10 does throw more shot down range. If choked right having said that, you should have more pellets on target. With the new shells hitting the market, so far the 12 has more speed. 1700 fps vs. a max of 1500 fps for the 10. That may change. The biggest difference for most is the weight difference. A lot of the 10 gauges are over 8lbs. My SP-10 has to be in the 10lb range. I don't notice the recoil, so that's a good thing..