I've always used skiing layers... as I've figured if they could hold upto a skier falling at 20-30mph they could hold up to a little rock scramble!
Usually a pair of silk under-layer, usual pair of exercise pants for mid layer & ski pants for outer...... used this set up on a bunch of climbs even upto 14,000' +
Of course if you are getting into a lot of technical rock / ice you might want to consider something that is a little more "snug" as the baggy ski pants do drag a lot while climbing vertical ice etc,
'when it starts to hurt your nearly halfway and probably should get out those ropes & put your crampons on"