Hey man, welcome to the forum. I can't give you exact numbers on the gas mileage but the XX can definitely ride that kind of distance.
http://www.atvriders.com/atvracing/score-2008-baja-1000-atv-utv-race-report.htmlCheck out that link. The 700xx is being raced in all of the Baja races and it is doing very well, it actually got 1st and 3rd place in the Baja 500.
Wayne Matlock, El Cajon, Calif./Marc Spaeth, Ramona, Calif./Rick Cecco, Briling Springs, Pa., Honda TRX700XX, 10:10:40 (43.34mph) (Class 25)
Javier Robles, Mexicali, Mexico/Adolfo Arellano, Tijuana, Mexico/Cesar Lopez, San Felipe, Honda TRX450R, 10:11:01 (43.32mph) (Class 25)
Danny Prather, Ramona, Calif./Mike Cafro, Bonsall, Calif./Chad Prull, Laveen, Ariz./Levi Marana, Hemet, Calif., Honda TRX700XX, 10:19:05 (42.76mph) (Class 25)