Actually the .500 S&W power levels put the 50-70 on the back burner, and I'm sure some maniac out there is designing a new cartridge with an even bigger BOOM.
Can't imagine it, my Redhawk in 44 has MORE than ample stopping power with more than enough recoil. Why kill yourself? I took 1 deer with it, just as quick and clean kill as a 06, dropped dead in his tracks 1 shot to the back of neck head on.