SWS20, the SPOT works fine even in the rugged cascades. I used it on a 5 day northern Picket traverse (little beaver-whatcom-challenger-fury-luna-access creek-big beaver) last summer and I was able to check in with my wife and kids at all locations, whether on the trails, while bushwacking or in the alpine. It would work equally well in 911 mode as well.
If going solo, one could get away with a pretty light pack as well. what does a soloist need beside a little clothing, stove, food, bag, foam, and siltarp? a 35-40L pack would be plenty.