The #3 will handle any loads up to about 44,000CUP range. You will find in the manuals that even loads listed for the Ruger, Browning and Siamese Mausers are usually held to about 36,000CUP. By judicious loading, you will be able to load your #3 .45/70 to where you won't want to shoot it due to recoil. Sticking with Elver action-type loads is probably a good idea. This will allow loads with 400gr. jacketed bullets to just over 2,000fps, and 350gr. to 2,200fps. Check out the data in Accurate Arms site or manal.
: A #4 will generally handle ammo loaded to approximately the same level as a .308 Wincester. We've used these actions for long range shooting in both .308 and more recently, rebarreled to .223.
; Some time ago, there as an article in "Rifle" magazine on an Enfield being re-barreled to .458 and chambered for the .45 2.4" case (.45/90Win). Either chambering makes for excellent useage for North American heavy game with easy to procure, resonably strong actions that are dirt cheap to buy.