By keeping your extremities warmer, you keep your core warmer, which translates to better rest. (I use the term "rest," because I find it rather difficult to do any better than rest--but, hell, good rest is still preferable to bad rest). It is amazing how far the hat, gloves, and down booties will go. It also depends on how long you plan to stop. If you are planning for (8) hours, you need more insulation. If, however, you plan to stop for only (2) hours on a summer alpine climb, you can leave some heavy stuff at home. Put on all the clothing you have in your pack; roll out your pad inside your bivy sack; jump in quickly before your body cools off too much. With hat, gloves, and down booties it is quite tolerable for a few hours.