I've ridden in the Rockies and only used a 24x23 low gear. Never needed the 24x28 lowest gear. It did not hurt me.Not sure where you rode in the Rockies, but I will say that the route that the OP is talking about has much steeper climbs than anything I saw in the Rockies on the Trans America.
Slumgullion, Wolf Creek, Red Mountain, Rocky Mountain Park, Rabbit Ears, Molas, Coal Bank, Monarch, Squaw, Berthoud, Vail, Loveland, Mt. Evans. The point of my comment was to point out that a 24 inner ring gets you a lower gear than a 28 ring. So with the same cassette, you will have one lower gear with the 24. Maybe you won't need to use it. You will be able to get by with the 24 ring and your next to biggest cog. Nothing is harmed if you carry your biggest cog and don't need it.