Welcome to the bestest in lumbar packs. The Mountainsmith technical series includes the Epic, Ultra and Sprint. The primary difference is how they carry water: 32oz bladder, dual 22oz bottles and a single 22oz bottle respectively.
I tested the Ultra because I wanted the dual bottle pockets for their versatility. I can carry two bottles for myself if I need that much, or if I do something stupid like the Crow Pass Crossing backcountry marathon I can carry one bottle and a filter pump. I can also substitute a can of bear spray or a medical kit: "Paging Doctor Daniels, Doctor Jack Daniels."
The suspension is so comfortable you will forget you're wearing it. Two plastic stays in an "X" configuration keep the pack suspended away from your nasty sweaty self. The mesh waist belt is both comfortable and breathable. All the usual smart features you expect from Mountainsmith are there too: reflectors, headphone port, high-visibility interior, shock cord for external carry and a four-point compression system. There are even two pockets on the waist belt, one with a velcro lid and one open for gel shots or a can of butt sweat: they taste about the same. Very minor quibble: the bottle pockets could be tilted forward for easier access.