My 2 cents (though I am known for my much lighter than average Big Bores)...Unless you are really recoil shy,or will be doing mostly bench shooting and not much hunting,go lighter!If your on a bench,you can always use the Caldwell Lead Slead when sighting in...I think you are correct in assuming a 3" mag 12ga is similar to a 9-10pd 458Win and a 3 1/2" would be closer to the Lott...Above post mention stock design,this is definitly Important too! I had a 13pd 600 Double that kicked way more than my 8pd 600 Overkill! Hard to believe,but true!To much drop,as in that double,can be brutal....anyway,if you are to do alot of African Savanna's and tracking spoor for miles in the hot African sun,you will be happy that your not carrying a 11-12pd rig that gets heavier every mile!...In Alaska after Brownie,again,go light as the mountain walking/stalking is much more "fun" with the lighter of choice....Most guys go for the longer barrels,brakes(removable is better)and weighted stocks...Not necessary in a 458 Win...The Lott is a little more thump,but no problemo!....Last,the lighter bullets are lighter in felt recoil for sure! Good Luck!