i lost so much weight in china that i now have to eat a candybar just to walk across the street! ifin yer wantin to go light and fast i highly reccommend a headlamp...if it gets dark where you are. no reason to stop for a bivy in terrain suitable for night travel. and a 20' whipper is really exciting at night, both for the climber and the belayer watcher a light coming quickly towards him. also it's really great in a dimented/spooky kind of way when the headlamp falls off and drops for a few hundred meters. that's when the fun bivy begins!