One day of climbing, or one climb and descent is unlikely to need much "manual transmission"
If you do all the flipping, flopping, and changing of chainrings, i would be interested to hear about your experience.
Since i am planning this insane ride across the U.S., fixed (Big Fix 2006) We will likely employ similar strategies in the Rockies, Sierra Nevada, Utah. www.fixhistio.org
But i agree that for one day, or one climb, pick your ratio, stick with it.
A bunch of us here in Nocal paln to ride a flattish century--4K ft of climbing, 3 longer climbs, and most of of will use 72-85 gear inches.
Have fun, spinning is winning, live fixed or die!