Hello from Georgia,
There is no doubt that a well placed shot at the appropriate range from a .444 will dispatch any game animal in North America. and, although there are pistol rounds more powerful than the old .44 Mag, it remains a very effective hunting weapon. As far as giving up on the 45/70, I simply can not understand the logic. The 45/70 is a true .45 caliber, and with the range of bullets from collar buttons to 500 gr. solids, this round is among the most versitile. The ability to load the same bullet in two guns is a good proposition, but if you are loading anyway, does it really matter. I encourage you to do whatever you feel is right, and if the .444 is in the equation, make it smoke. As far as getting rid of the 45/70, I would encourage you to get a little more familiar with it before you decide. I as well as lots of others here would suggest you keep it even if it were behind the .444 on your favorite list. Good luck, and keep on shooting, one shot at a time.
Dave