> Got a waterwheel doing 1000RPM and you need a big saw attached to it? Your saw will be running at 1000RPM (~16Hz).

Most "waterwheels" turned far more slowly than 1000 rpm. More like a few hundred at most. They used pulleys and belts, and eventually CVTs.

Edit: http://www.alternative-energy-tutorials.com/hydro-energy/wat...