Well with 36/25 I can get the same low gears I can with 39/27. I think with 12/27 and 50/36 I will be sacraficing some speed, but it will be on the downhill. On the uphill I will be gainning an extra easy gear to spin. On flats I usualy spin in 53/14, so I won't be loosing any speed there. Basically I think it will be a gearing for Mt. Hamilton.