Troy,

totally depends on the weather, IMHO. I've flown right across the Tioga
pass in a Bonanza (more power, admittedly) without O2, but the weather
was REALLY benign. The Mammooth pass off the Fryant VOR is very well
doable, if the winds are low (and the temperatures not too high). If
they aren't, your option is to go further south.

--
Thomas Borchert (EDDH)