Many factors need to be taken into consideration when deciding on the size of your turbine. It is not enough to compare power ratings alone, these ratings are determined at certain wind speeds which are normally higher than what the turbine operates at.
The best method is to consider the size of the blades, which in turn is related to the size of the rotor. For example the Evance R9000, whilst being a 5kW turbine, can out perform a 6kW turbine at average wind speeds.
To decide on the turbine most suited to your needs, Dorrell Renewables needs to take into account the following; your budget, your electricity needs both current and future, and also most importantly, your site.