I don't know...
A No.1 in 500/450No.1 Express in the classic English sporter style
would be pretty sweet.
I don't know what a good smokeless load would be
but my 1869 with 85grs of black and a 460gr cast bullet
is quite accurate and a pleasure to shoot.
In fact, I have a Metford rifled barrel and an 1881 action just
begging to become such a rifle.