Connecting the turbine to a generator will slow down the rpm.
Using a gearbox to increase the rpm is like shifting to a higher gear on a bicycle. And, connecting the turbine to a generator is like riding your bicycle up a hill. If you go to too high a gear, you will not be able to pedal up the hill, and actual rpm becomes zero. Likewise, using a gearbox to increase rpm could actually make the thing run slower (or even stop) when you attach the generator.
There will be an optimum gear for a given wind speed.
Given the low winds you are working with (2-3 m/s or 4-7 mph), you would require a relatively low gearing, compared to having the same turbine in say a 15 m/s wind.