I suspect that this is far too complicated to come to a sensible answer.
In theory rpm will be determined by rotor diameter tsr and rated wind speed.
In theory gearing doesn't affect the rotor rpm but as it affects the alternator rpm there is bound to be an interaction as it is possible to make a smaller and cheaper and usually more efficient alternator for a given output if you run it at high speed.
Rated wind speed will affect the rated speed as a higher rated wind speed will result in higher rotational speed even if you keep the same tsr.
A manufacturer claiming a large maximum power out and rating at say 30 mph will probably need to aim for a higher rated rotational speed than a lower power rated machine aimed for say 20 mph. On many sites the higher power rated machine will produce no more power but it will sell better as it boasts a higher rating.
The other factor that has a lot of effect is how the alternator is matched to the blades and for what wind speed it is optimised. An air gap type alternator matched for a low wind area will likely have a low operating speed at full rating and may be approaching stall at rated power. A machine using a slotted cored alternator with the same cut in speed may well be approaching reactance limiting at full output and may have double the operating speed at the same rated wind speed. Whether it produces more or less power depends on too many factors.
If we remove many of the limitations and compromises of normal machines and consider those whose rotational speed directly tracks wind speed ( constant tsr) then there would be far less variation. Most would choose the highest tsr that would let them reach the rated power at rated wind speed with an acceptable noise level.
Things may be changing but in the past there was a tendency for makers to go for high rated power and accept that it would have to come from higher wind speeds than most people are likely to see on many occasions. They were not often too bothered that at rated power the things were by my standards very noisy.
Home built machines are more often designed for better performance in low winds and the common use of air gap alternators has meant that the full power operating speeds are much lower than the early commercial machines, They produce more energy on most sites for a given rotor diameter, do it with less noise and stress, and to some extent some of these ideas are rubbing off onto the commercial manufacturers.
When mppt becomes common, one of the effects will be that to gain the best from it, top speeds will need to rise again and more attention may be needed to obtain these higher speeds with good aerodynamic efficiency and low noise.
While we bog down alternators at constant volts the type of alternator will continue to have a large effect on the running speed.
The slotted iron cored machines will probably produce similar outputs from fairly low efficiency alternators using the higher prop efficiency. The air gap machines will need to be mismatched sufficiently to keep the blades from stall and will produce similar outputs but with higher alternator efficiency and lower prop efficiency.
The cheap alternator with slots and lower efficiency at full load may manage a better full output as it will be able to dissipate the losses in it far more effectively. Often it doesn't need to furl very effectively to survive high winds if it reactance limits and you may find it running at relatively higher maximum speeds.
What speed is really best will be more dependent on the site and local wind conditions than the whims of the manufacturer.
Flux
