I believe that the Fenix E0 should have no trouble living in the desert environment, but I am unfamiliar with the wear and tear the desert may cause on lights.
With flashlights it tends to be that you get what you pay for, but as you go up in price you get less value... I believe that it is generally agreed that Peak and Arc are on par, and Fenix appears to have made a "better" design, utilizing a spring in the body to prevent the circuit board from being crushed due to over tightening (a rare Arc problem)... and with better regulation.
On the other hand, there are those who believe Fenix quality is suspect, as the lights are manufactured in China as opposed to the USA. But Fenix has also shown that they are not your average Chinese manufacturer, opting to improve the products over time, listening to the consumers, and generally offering a great product with excellent value...[/QUOTE]
I found a review on the Peak Matterhorn 1-LED:
http://www.flashlightreviews.com/reviews/peakled_matterhorn_ultsnow.htm
It looks as though the light quickly diminishes to 50% brightness after about 3 hours. However it will last around 10+ hours around 30-40% brightness.
Now as for the Fenix E0:
http://www.flashlightreviews.com/reviews/fenix_e0.htm
The light last at about 100% brightness for around 9 hours. 50% after 12.5 hours. And gives a good 14+ battery life.
For durability, both lights (along with the Arc AAA) are made with machined aluminum with type III hard anodize finish. So they all seem about equally durable according to reviews.
As for the brightness. Not too sure about the Peak Matterhorn, but here is a comparison between the Fenix E0 and the Arc AAA-P:
http://www.wubin.net/flashlight/fenixe0arcbeam.jpg
Looks about the same to me. Fenix E0 looks like the better buy according to reviews. Of course you guys are the pros so i'm leaving the final word up to you.