I'm much closer to sea level here in Georgia. You are correct, altitude plays a factor because the air is less dense. There are a number of ways to compensate for this (higher nitro content, bigger engine, lightening up the plane, etc). Although I lived in Albuquerque, NM for a number of years, I did not fly R/C then so I have no personal experience. However, many people on these forums do and they can offer you some excellent advice. You could probably do a search on "altitude", among other things to find answers. Hopefully someone will chime in here to give you a hand to help you understand. I'll just end up confusing you. Like others have pointed out, there is a tradeoff when you add weight to a plane (by going with a bigger engine, for example). You increase the wing loading for one, which changes the flight characteristics of the plane. If it flies the way you like it to fly, it doesn't matter. That is the most important thing. In my opinion, you'd be better off using a 46 size engine, along with keeping the plane as light as possible. The 75 might work just fine, you'll have to try and see. I'm all about having too much power and managing the throttle to keep things from getting out of hand, but too much wing loading can be a problem.

I almost guarantee that there are some people that have used a 75 on this plane and loved it. Hopefully they will give you some help to get this combination to work. I understand budget constraints, you have to do the best you can with what you have and what you can afford. I better shut up now before I get you in trouble :-).

Thanks,
Gary