I have both. For the fun of it and the nostalgia of it it is hard to beat a 45/70 period. With it you can run a 15 inch barrel to slightly over 2000 fps with the 350 Speer to over 1500 with a 550 hardcast.
Wide variety of loads for the 45/70 from trapdoor levels to the lower 40000 cup range. Cheaper brass, easy to find bullet molds, etc..
Only thing is that recoil in a 15 inch tapered unbraked barrel is off scale with a violent whip. I have more powerful calibers set up with a bull barrel and a good brake that are more comfortable to shoot.
Would a deer or even an elk know the difference between the two I hardly doubt it though.