As we discuss different possibilities, I would suggest that each venue
has its own attributes and problems - heat, cold, wet, surface breakup,
I would not view a site around 5000 feet as a reason to avoid an
otherwise good/better location.
I ran in Colorado about ten years ago (The "Durango GP") with a
carbureted MGB and it was not an issue for me. While I am not as fast as
some of you (disclaimer), I would think that those "at the top" could
easily handle a jetting change *if necessary*, to avoid chunks of the
course breaking up and a strong chance of wet weather.
Every possible site will have some issues, so we have to judge the whole.