You say you want a "light handy deer rifle for carry around", and you have a .45 caliber Puma 92. It seems to me that you have what you need. I assume that by ".45" you mean it is .45 Colt. The 92 action is plenty strong, so you can shoot some very stout .45 Colt hunting loads out of that rifle, and the 92 is about the lightest, handiest repeating rifle around. With the right loads, you could easily take down large whitetails at up to 200 yards with that rifle.
The 45/70 is a much larger cartridge, and fires a much heavier bullet. While you theoretically have a longer reach with it, ask yourself whether you need or would ever use that reach. And keep in mind that the 45/70 doesn't really move significantly faster than a .45 Colt, so trajectory will be comparable -- the 45/70's extra hitting power comes from the massively heavy bullet.
So going to the 45/70, you get less mag capacity, a heavier and less handy rifle, and heavier recoil, and for what? The ability to throw a really heavy bullet you don't need.
Frankly, I think the Marlin 1894 in .44 Magnum is the best choice for a light, handy deer rifle. If you really dislike your Puma, look at one of those.