The only way you are going to be able to shoot at 200 yards is with one of the premium sabot slugs. They are going to be launched in the 1800 - 1900 fps range. Even those do not have the best trajectory over 200 yards. But if you do shoot that distance with a 150 yard zero you are going to be hitting about 3.5" high at 100 and about 7.5" low at 200 and starting to drop off fast. The 20 ga is going to be in the 800 f/p range as far as energy is concerned at 200 yards. The 12 ga is going to be more. I think the 20 and 12 will shoot pretty close to the same. I am not sure if the 12 ga would have a better trajectory or not. It is a heavier bullet, but is bigger in diameter, but of course will have more energy. The 12 has a heavier bullet and launches at about the same velocity. I think it comes down to how much recoil do you want to deal with and how much energy do you want out at 200 yards. Some consider 1000f/p the minimum for deer. Of course projectile placement is the most important thing and when you have that much drop, you had better know how far it is. Some shoot the lower recoil better. I think it is a toss up. How well you handle recoil would be the deciding factor, the 12 has considerably more than the 20. just my 2 cents
