How badly do you want to get faster?

Speedwork is the only thing that's ever made me faster, on the bike or on foot. My long run pace is considerably slower than it was when I was running shorter distances. I think one interval session a week would be plenty to see improvement, if you're consistent about it.

V, seriously, if you haven't tried the Nathan Intensity pack, give it a try. It rides SO much lighter than my waist pack and interferes with my body mechanics SO much less, that I prefer it even if I'm only carrying an hour's worth of water. I wouldn't even consider running in my Platypus packs or my DH's Camelbak - this is a completely different animal. As Yellow described it, it wears like a vest, not like a pack.