I think the 450 Marlin, although another excellent choice in this family of big bore powerhouses, has no advantage over the 45-70. Some might argue that it is in fact at a disadvantage due to very limited bullet selection and longevity concerns.
My recomendation would be to pick up a guide gun chambered with the cartridge that has proven itself as the big dog of the big bores for over a hundred years.
At the same time I would welcome either a .444 or a .450 to my collection with open arms. All three are class acts that will do the job superbly.
Now if Garret or Buffalo Bore decide to come out with some 450 Marlin rounds of their own the decision would definitely get more difficult.<img src=icon_smile_tongue.gif border=0 align=middle>