If you do plan to stand on a hill and are riding in a line, PLEASE announce your intention to the riders behind you. If you don't do something to maintain speed as you stand, it will, to the rider behind you, likely appear as if you have shifted into reverse; you'll hit the trailing rider's front wheel in all probability. That generally puts him on the ground, hard. A bit of warning reduces the risk.

34x25 gets me up the steeper hills around here at a nice clip; I try to maintain ~100 rpm or a bit higher as long as possible.