577 will require special registratio/permission/taxation as a destructive device.

I'd take a 5-shot 500JRH built on a Redhawk.
500JRH has taken all of the mad bovine, including Cape Buffalo

Redhawk is far more handy than the X-Frame Smith.
Far easier to carry, much more compact.
I've shot full hit loads through a 2" Alaskan conversion, and it was surprisingly controllable.
Personally I'd go with 4"-5" of barrel.