wilderness athlete makes some supplements designed to help altitude aclamation.....something to try if you're concerned or have trouble with altitude.

don't want anyting to slow you down? haha good luck with that altitude, its tough, I'd say take it slow the 1st day, see how things go, don't plan to jump off the horse and run up those mtns.

Certainly helps to be in great shape, the better you can be the better off you will be, but those guides running around the mtns all day, and us lowlanders are 2 different things.

I'd take a look at your pack etc....and try to figure out ahead of time what you'll need etc...and lighten up your load as much as possible. Everything adds up....a pound here, pound there.

Maybe have that pack ready to go before you even land in NM, staying up late figuring out what you should bring or not etc....can cost you time/energy, waking up at 4am....etc...

but good luck, have that rifle dialed in too, I'd assume dead on at 200yds, and hopefully can take some 300 and 400yd shots before heading out there.

If going on horseback....talk to the guide about scaboards, and you might want to buy your own....