As a follow up post, on another thread I used this example about the added muscle. Go out, do yourself a nice 30-40 mile varied terrain route and note your results. Now clone yourself and get a tandem. You and your clone mount the tandem then do the same route. The tandem version will have totally different results than yourself. Despite being twice as heavy, the tandem version will be significantly faster in the flats. But on the hills and climbs(because of the weight) will struggle and be searching for more gears.