Cool topic, and one I am familiar with.
If we look at the old 45-90 Sharps and the Modern 458 Win Mag you will see both shells are the same length. 2.5 Inches.
The 45-90 had a wonderful reputation in its day. Shooting big heavy bullets at only about 1300 FPS, they were very accurate and killed anything they hit.
I have found the 458 Winchester to be all the shell a hunter could desire as long as he knows the range to the target and the trajectory of his load.
The cool thing about the 458 is that it's easy to get an accurate load with velocity in the mid teens. 1400 to 1600 FPS beats the old BP loads of the Sharps and Remington fame of the 1880s, and they will shoot from end to end on elk or moose.
I have loaded 85 gr of black powder in my old Winchester M70 with a card wad, a greased felt wad and another card wad using a 450 grain LBT bullet and with that load the rifle would hit a 50 cent piece at 100 yards EVERY time.
If you are going to build up a rifle for such loads use a Pac Nor or green Mountain barrel cut for lead bullets. The rifling of these barrels is a bit deeper than it is for barrels made for jacketed bullets.
If you are simply going to buy a rifle in 458, you need harder bullets to hold the rifling, but they can still be wonderfully accurate if you cast the bullets correctly.
A Modern rifle with a modern scope that duplicates or slightly surpasses the King of the old BP Cartridges....what's not to like?