To drive home the point in comparing .45-70's to the .416, note that the .458 win with a 400gr load in Trophy Bonded Bear Claw by Federal shows an almost identical trajectory:
http://www.federalcartridge.com/amm...firearm=1&bc=0.381&muzzvel=2380&bulletwgt=400
The point of the comparison is that the energies of the .416 Rigby are very much in line with those of the .458 win. This implies that all the comments comparing .45-70s with the .458 win hold up well.
HOWEVER, to give due credit, penetration has much to do with the construction of the bullet, as well as the energy. Softer bullets will tend to mushroom or explode at higher energy, giving less penetration than lower energies (paradoxically), BUT, in the process, will do more damage to the tissues where they hit.
One good comparison and some more detailed discussions of these points is given in:
http://www.freerepublic.com/focus/f-news/1011537/posts
At higher energies, cast bullets won't make it through a barrel at .458 or .416 energies, but will if you reduce the charge. Paper patching can give you more flexibility with lead bullets. Harder bullets have more tin (and other metals). This looks much like old lead solder -- it can "tin" your barrel (the metal binds to the inside of your barrel). Even with lower black powder charges in a .45-70, there's a risk of that... BUT, people have had good terminal ballistics with hard-cast bullets at lower energies -- can't argue with success. But, I've been very curious to hear whether anybody has noticed (or cared about) tinning in their barrels?
Dan