I use a Beal 30m 8.0mm twin rope. Bought it that length. The purchase was for simple glacier travel with 2-3 people, but I've used it in the Sierra more.
I don't use it if there is a true vertical lead, but it is absolutely perfect for what you just described. On Humphreys, for example, it was only for the downclimb if needed, and rappel stations were set up for a 30 m rope. Same with Clarence King.