The .444 is great for deer and black bear and I expect elk as well but as I have never had the opportunity to hunt them I can't say for certain. The .444 was introduced in 1964 and does a good job at bringing down the deer.
I would personally recommend going with the 45-70 as you have a much greater variety of ammunition available to you and over a century of proven usage with improved ammunition increasing the effectiveness regularly.
The .450 Marlin really has no advantage whatsoever over the 45-70 considering some of the hotter factory ammo that is available and, like the .444, it is limited in the variety of available loads. The .450 Marlin is also a newborn in the ammunition field so it's staying power has not been determined. You wouldn't want to buy a firearm that you won't be able to find ammo for in 10 or 15 years. Not that this is the case with the .450 but at this point and time noone can honestly say what the future holds for this round.
Again I recommend going with the tried, proven, and very much available powerhouse known as the 45-70 Government. There is nothing you will hunt in North America that is beyond it's ample capability to bring down hard and fast.



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