Just had a thought as I was stuffing some extra "emergency" layers into my pack, mentally weighing each piece as it goes in...
Ever thought about forgoing emergency layers (if you even bring em) and just taking a nice lightweight sleeping bag and emergency bivy sack? My 20* sleeping bad and SOL emergency bivy bag together only weigh about 2.5lbs... I'd have to think, if stranded at altitude in the wind/precip with a broken leg waiting for rescue, or even just snow-graving bad weather, I'd probably be overall warmer cozying up inside those than throwing a bunch of layers on.
Obviously the bags won't help much if you're trying to egress crappy weather, but for spring/summer climbing, any totally unexpected weather that rolls in will be violent but quick- thunderstorms, basically.
Anyway... just a thought that crossed my mind. Yours?