I have the same gun and don't recall Henry having any statement about the gun having an extraordinary capability. You load by the book. It's a 45 Colt and within that spec I don't expect it is a deer rifle at any sort of range. You would expect that it should be good for at least tier 2 loads, say around 20k psi, but how does one really know that other than asking "hey, do any of you have a 45 Henry you haven't blown up yet? Whatcha shootin in it?
What reliable rule of thumb says a rifle is any different than a handgun in the same cartridge? Who says they would all comply with someone's rule or experience.