I have riden geared bikes for years and cycle mainly around the cotswolds, where fixed would be no use. I have a Bianchi and normally go out and cover about 25 - 55miles, using the gears to keep my cadenance and heart beat within small range, for fitness, cycling on my own. Then I started working on the Olympics and by far the best way to get to work was cycling, not wanting to bring my expensive bike to London, I bought a cheap single speed machine. It is 4miles each way to work and i did it every day, including weekends, for 4 weeks. Being fairlly sensible i did not jump every red light or dart on and off the pavements to reduce my stationary time, some would say this takes away the fun of the machine but it meant I had lots of starts from being stationary. And I wore a helmet, which doesn't look cool on one. But I loved it. My point is that when I got home I went out on my usual bike and could not believe the increase it made in the power I could deliver, both in acceleation and climbing hills. Over 40miles it made a big difference to my times and average speed. I'm back for the Paralympics and cannot wait to commute to work again for the next month.