The Champion 3500/4000 will start our A/C with just a bit of grunt at 10,000 ft if the converter is off. I wanted a 2800w inverter generator but was told they are limited to around 8000 ft before they lose the ability to run the A/C. Ours works for us as we boondock without neighbors.
The Champion 3100i is said to have more surge ability than the Honda EU3000is, is much less expensive but is also louder both in eco mode and under load.
Changing the jet will make the generator run cleaner at altitude but wont replace the thinner air. You will still have to deal with the loss. (up to 40% on a hot day at 10,000 ft)