I would suspect on one level there's an equivalency but body weight fluctuates while a couple of pounds off the bike won't have any fluctuations; every upgrade in performance is an upgrade that will see you faster every ride until something like bearings get worn and need replacing or repacking. While the body weight can be canceled by a pint of Ben and Jerry's while snuggling with the wife. On the other hand if there is real weight to lose the benefits lie there; thinner people are more aero not to mention the other health benefits that will make you faster. But lets face it, I'd have an easier time dropping the weight from the bike and can still work at dropping it from the body.