In reply to monsoon:
For winter I go with the smallest pack I can get everything, (with the exception of ice tools,) inside. This is 35l for me, although with a big mixed rack and belay jacket it does take a bit of careful packing. The reason for this is to keep everything waterproof if you need to walk up through rain. I'm not as worried on the way out so if the weather doesn't allow careful packing I coil the rope in loops and throw it over the top which generates enough internal room to pack in a more 'chuck everything in' fashion.
I'm not a great fan of putting crampons on the outside of a pack having had a friend who once lost some as a result of doing this.
My 35l sac, made by Aguille, is really light, (while still very tough,) and compresses really well for climbing. I don't think I'd gain anything in freedom of movement / less faff etc from having a smaller main pack, (although I do sometimes take a 15l rip stock pack with me to use for a belay jacket, map, compass and torch, carried by the second, if we are returning to the crag base so don't need to climb with the main pack.)