RE: 20 guage or .12 guage slug gun?
A 20 may or may not outperform a 12 accuracy-wise, or in any other way. This is a very individual thing, andvaries from gun to gun.
However, a good20 with these new type slugs is plenty accurate enough, and has more than adequate energy to be fine for deer hunting. After all, a 20-ga. is.60-caliber, and firing a 385-grain.600" slug at velocities in the vicinity of 2000 fps is not too far behind the .600 NitroExpress, except as regards bullet weight! The 600 Nitro fires a900-grain bullet at 1900 FPS; the 20-ga sabot slugs are about 1/3 this weight, and at a comparable muzzle velocity. An elephant weighs more than 3 X the weight of a whitetail deer, however! Deer also have much thinner skins!