I think bike weight (and rotating weight) has a bigger than proportional effect on performance. I perform better on my Swift than on my heavy R20, and can't be absolutely sure about this but perhaps the effect of the extra weight that I have to handle is to put a subtle psychological block such that I don't feel like working as hard. Like a placebo effect? On the Swift I feel fast and strong and like to go like stink, on the R20 I feel like I'm lugging the world on a chain behind me, so I can't muster much effort. I think.