In reply to JayPee630: I haven't tried running with it, but it's a "soft" pack and doesn't move around. Not sure what you are looking for in a running pack to be honest?
Have you looked at the camelbak range? I know a lot of mountain bikers and runners use them in endurance races. I have a small one which has been used for moutain biking and snowboarding for over 10 years and it still looks like new (when washed!) TOUGH packs, and as I say, seen plenty of runners with them. Nothing quite as large as you want though, although they do them.
Actually I wish I'd looked at their new range before deciding on the Medusa, there might have been something in there that would have suited me.