"Well, that really depends on where the OP lives. I live at 5400 ft, and work in the woods off trail between 4000 and 7100 feet. When you're used to it, an ounce feels like an ounce, not a pound. And I have no doubt some of the true mountain dwellers would read what I just read and say , "Try 10,000 feet and then we'll talk."
I will admit though, you are looking at it from a flatlander's perspective so 6000 feet probably feels different. When ever I go hiking in the lake states, I am amazed at how fast I can move and for how long. Oxygen is plentiful there..... but so is humidity. "
I'll confess to being an eastern flatlander...hehehe. I can associate with altitude you are speaking of. I feel it most starting about 11,000, more specifically on a long steep climb. What I find less desirable is humidity below 7000 feet.
As far as the revolver goes, I'm not an Ounce Nazi so I'd go with the one I shot best or even carried better in a holster with the pack on. An extra shot doesn't mean much to me since all my revolvers are sixguns....well one 5 shooter as well..