You can use heavier slugs in the 45-70 than in a 375jdj .You CAN practice out to 200 yards with your gun using 300 grain soft points.Velocity can reach 1900fps,but recoil is way up there at this speed.
a 300 gr .458 started at 1900 fps will still have 1069 lbs of energy at 200.
sighted on at 150yds,it will be+2.2"@50,2.9"@100,0.0@150 and-7.4"@ 200.
considering the size of the vital area of a moose,I'd stick with the gun I am used to.Besides ,you can buy an awfull lot of practice bullets for what a new barrel costs.
But heck ,buy the new toy .You need some thing small for varmints anyway,don't you? jh