You are correct, they kick like a really POED mule. Unless one is hunting large dangerous game, there is probably no need for a 3" magnum slug load. Of course a lot depends on the type of action being used, the stock on the weapon, and the individuals ability to use proper stance and absorb recoil. I used to be able to take my AYA 10 gauge double(18.5" barrels) and fire both barrels at once just to prove recoil did not bother me(3.5" magnum 000 Buckshot). Now as I am older (and wiser) I let others macho out, and try not to show pain.
Remember that even with a standard load sabot slug, you are putting out a 50caliber slug at fairly high speed. That should do it for anything you might meet around here(or there).