Colorado - your 12 would do just fine. One has a difficult time realizing just what that 'type' power is like, until one shoots these guns themselves.
: Years ago, I chopped the barrels on an old "Fluid Steel" double shotgun I aquired for $75.00. I chopped the barrels at 24" & worked on developing loads for it using round balls, both hard and soft. I developed loads right up to the max ctg. 12 bore load of a RB with 191gr.2F, and chrono'd that one at just over 1,550fps from it's short 24" bls.
: I inlet a sight in the middle rib, and then regulated the loads to print to the sights. I even mounted a scope to eliminate any miss-sighting on my part. I found that not only did the light charge of 150gr. shoot to the sights, but so did the heavy load and most of the smokeless duplication loads I tried.
: When matching the BP velocities in smokeless, I found SR4756 to work beautifully, giving a requisite dup1ication load of 1,550fps with the 545gr. RB & at a greatly reduced recoil compared to the black powder loads. It was the best case senario I could hope for. With the smokeless loads, it kicked no more than a 1-1/2oz short magnum shot loads, yet pressure signs showed les overall presure than even the BP loads.
: Out to 50yds. it was deadly accurate, like a rifle, throwing both barrels together and grouping pretty much parallel for 4" groups. At 100yds. I could consistantly hit a 12" plate, standing, lefts and rights consecutively and man, did it ever bounce that plate, up, down, back and forth, sideways and back again. The plate was a full 2-1/2" thick & weighed about 50lbs.
: At the range one day, a fellow was shooting his brand new, "super powerful"(his words) 7mm mag, developing at least 800 more FPE than my 12 bore, yet his 175gr. bullets barely moved the plate back and forth. He was quite confused when my next shot, visibly impacting in the plate's middle, broke the heavy chain holding it up & slammed the plate to the ground. Of course, he knew little about momentum, a feature much neglected in modern ballistics equations.
: I could never figure out how something developing 3,500FPE(or more), would barely move a 50 lb. plate, yet a .68" RB from a front-stuffer at only 1,300fps, would make it bounce. BTW- that's only 1,800FPE.