After checking out the fit/finish and construction of both the Viper and the Raptor series packs I ended up going with the Viper 10, the upper middle of the size range for the Viper series they are available in sizes 4,7, 10 and 13, each number representing the liters of "stuff" they can carry as opposed to water volume. It struck me as a bit of an odd way to measure internal capacity but their website does convert it into cubic inches. For comparison the Viper 10 (610 cubic inches) is just a bit smaller than the Camelbak M.U.L.E (763 cubic inches), the Viper 13 is a bit bigger (793 cubic inches) but both carry 3 liters of water. I am not sure why but even though the Viper 10 was only slightly smaller than the M.U.L.E it felt like a much more compact pack. I have three Camelbak packs but after using the Osprey I might be a convert... at least for new pack purchases I'm not going to just trash the ones I already have, that would just be almost as financially irresponsible as the government. The Viper does have some features that I really like more than those on my Camelbaks.
Probably the coolest feature that the pack has as far as I am concerned is their Lidlock helmet retaining system.
There is even a drawstring so you can increase or decrease the tension on the Lidlock.
Two of the other features I thought were superior to Camelbak you really can't see in pictures but both the bladder and the pack itself have an internal piece of plastic that helps to maintain the packs rigidity when used without the bladder and the plastic in the bladder helps to make sure that the water in the bladder is distributed evenly during riding rather then pooling in the bottom of the pack like a half full Camelbak bladder tends to do.
There is still much more testing to do but as of right now I am kind of digging the pack and would be the front runner if I were looking for another pack. If your in the market for a new pack I would recommend checking out an Osprey as well, although I am not sure where you can find them around here so you might have to get one online unless your like me and have to be able to fondle it first. It'd be nice if one of the LBS would start carrying them, I really don't mind paying a little bit more for something if it supports the shops in town.