Does anyone know the weight savings as you move up the grades of Trek alpha alum frames. On a hardtail mtb the Trek 3000 series uses regular alpha alum. The 4000 series bikes use Alpha SL. the 6000 series uses Alpha SLR . and finally the 8000 series bikes use ZR9000 custom alloy. I know a lot of my weight savings will come from components ie forks, rims, tires, brakes ect. But the frame weight I start with is what I'm interested in.