The power you can get from the wind depends on the sweep area exposed to the wind covered by the turbine blade (either vertical or horizontal), the densitry of the air (dependent on the altitude of the place, temperature and humidity), and the cube of the wind velocity. Velocity is the main element of wind power.
Vertical axis (savonius, darius, drum type) rotors spin slower because the blades only work half of the time (180 out of the 360 degrees) while horizontal axis rotors work all the time because they are exposed to the wind throughout their rotational axis.
For a simple twisted blade shape for horizontal axis rotors, smaller rotors will spin faster than larger rotors. This is why gear boxes are needed for large turbines to translate the sharft speed to 1800 or so to reach the dynamo RPM requirement.
Multibladed turbines (farm wind pumps) will start spinning at low wind speeds because of its high solidity compared to two to three bladed turbines for electricity generation. However, multibladed rotors will only reach a certain RPM and not spin faster because the blades will be "shadowing" each other at this speed, but with high torque. Few-bladed rotors will require a higher starting wind speed but will spin faster than the multi bladed rotor at hight wind speeds. This is ideal for direct-drive wind electric generators with low torque requirements.
Wind in urban areas are turbulent (constantly changing direction and velocity) and vertical axis turbine seems to have higher tolerance than horizontal turbines. Ideally, turbulent places are not good for wind turbines because they produce a lot of mechanical stresses to the wind turbine. Minimun turbineshaft-blade Diameter ratio is 1/10, but safer for 1/8.
Making small wind turbines in a DIY way is like kite flying. You do it because you like doing it, but you don't do it all the time. So, enjoy kite flying ... or making small turbines.