Given the proper twist in either and identical actions the .405 would top out around 400gr. with descent speeds, while the .45/70 would do 480gr. to 500gr. at about the same speeds.

There would be little to prefer in one over the other, although I'd rather have a .405 in an 16" to 18" twist, just because. (I've had quite a few .45/70's or equivalents, time for something new)