I'm into randonneuring, so average speed is an important metric for me, which I realize is not the case for everyone. For the kind of recreational distance cycling I do, body weight is much more important than bike weight. I let my weight get up to 215 several years ago, from my normal 165. My lightest brevet bike is around 20 pounds, my heaviest is almost 50. I can say with absolute certainty that I am faster as a 165 pound human on a 50 pound bike than a 195 pound human on a 20 pound bike. At the same weight, I'm only marginally faster on the lighter bike if the course has a lot of big hills. Flat or rolling course, average speed is pretty much the same on a 20 or 50 pound bike. I rode a flatish 200k a few weeks ago on my 50 pound bike and stayed with the same group of guys I normally ride with on my lighter bike. If average speed is the metric, bike weight is just not as important as fitness.