Will,
The of all guns, the Ruger's will take truly hot 45-70 reloads. Built like a tank in that regard. "To stand out" is tough. You can just ream the chamber and come up with quite a few. Here is one possible list...
45-90
45-110
45-120
450 Ackley Magnum
450 Alaskan
450 Marlin
450 Nitro Express
450 Smith
450 Watts Magnum
457 WWG Magnum
458 Lott
458 Winchester
458 SOCOM
458x1-1/2" Barnes
458x2" American
450 Ackley Magnum
450 Assegai
450 Number 2 Nitro Express
450 Rigby Rimless
450 Black Powder Express
450 Nitro Express
450 Nitro Express 3-1/4"
460 Weatherby
577-450 Martini-Henry
Personally, I would go for the 450 Nitro Exp. 3 1/4". Not for any particular reason except it is such a "traditional" big game round.
Pete
