I would recommend Panasonic.
All of their panels (other than the 103") are rated to 9100 feet before they buzz or are no longer covered under warrenty. It is hard to find this in writing on their US site so I have supplied a link to their global site FAQ page.
You will need to go to question 9 and convert the meters to feet.
One might ask if this is reliable for the US market, the answer is yes as all the panels come from the same factories and are built to the same gas charging levels. Feel free to call Panasonic at 800-211-pana and they will get you in touch with a plasma expert who can confirm altitude for you.