In reply to Pipecleaner:
Have you tried looking at Skimo race packs/vests?
Dynafit, CAMP, Ski Trab, Crazy Idea all do something in the 8-20l size range and most have somewhere to store an ice axe, some have crampon pockets which you can access without taking the pack off. All super lightweight and ideal for running with.
I have the Dynafit RC 20 and have used it for both running and Skimo races, the Race pro is smaller and maybe more what you are looking for?
http://www.dynafit.com/en/equipment/packs.html