First the frame on the SBH is the same frame as the BH and Bisley models. Other than the gripframe, hammer and the cylinder on some models, they're all the same (trigger on Bisley diff too) The SBH actually has also been chambered for the .41 magnum and the .45 Colt cartridges as well. Both were Hunter models made exclusively for Davidson's and Lipsey's respectfully.
Remember if you can't hit what you're aiming at, bigger and "badder" makes a big imprssion alright - embarrassment. Concentrate of what one can accurately shoot not so much on the awe factor of a large caliber or powerful cartridge.bigger is fun and bragging rights are fun too
Custom 'smith have been rechambering the BH and SBH's from a long time now. .454 Casul chamberings are considered small now as they're now being safely converted to .500 maximum and many in between. A new cylinder (5 shot) and new bbl is required. It's mainly the cylinder taking the pressure more so than the cylinder frmae itself. 5 shot cylinders provide more material between chambers. More material allows higher pressures.
Check out Bowen Classic Arms (the master), Limbaugh, Clements, Cosby and Reeder for what is possible.