I run 85 all the time, even have my timing bumped up a little. 85 does have 10% ethanol everywhere here, but there are a few pure-gas stations around that have 87 or 88 octane pure-gas. I know of two at least in the great state of Northern Colorado.
I would stick with the 85 though. 87 or 88 octane pure gas runs nice, but is expensive and only slight gain in MPGs (negative return on your investment).
It should be fine with the elevation change and such.
I know in my motorcycle (a 2000 GL1500 Goldwing) riding two-up and towing a trailer ran it without ANY issue in Utah, and it also calls for 87 from the manufacturer.
Air loses density as altitude increases, which results in lower cylinder pressures (like lowering compression ratio) so an engine that requires 87 octane at sea level will tolerate lower octane at elevation.
In addition to this, most engines will respond well to additional ignition timing and a leaner air/fuel ratio as elevation increases.