It also depends on the terrain you ride. If you ride a lot of hills or rolling terrain, you will definitely notice that a lighter bike is less effort to haul uphill, but the change in body position may not make that much of a difference. If you ride flat terrain at a good clip, body position makes a big difference.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett