What are you trying to do? None of this made any sense and I have looked at an earlier post and I see that you are aiming for grid tie.
I think you are getting lots of things mixed up. With battery charging where you are clamped to a fixed voltage a good compromise between electrical and prop efficiency is to let the efficiency fall to 50% at about 3 times cut in speed. I am fairly sure that is what Ed had in mind.
It is also true that you get maximum power transfer when the source impedance is equal to the load impedance and that would bring the source ( alternator) to 50% efficiency.
Now under ideal working conditions where you are not tied to a battery or fixed voltage you should keep the alternator efficiency as high as you can. Once you let the alternator efficiency drop below 70% you start to run into trouble with heating in the windings. Big commercial alternators run at over 95%, but you won't manage this level in small ones with rectifier loads.
With grid tie the inverter should let you run with volts rising roughly with wind speed so you should be able to keep efficiency high. If the load resistance is equal to the source resistance you will be at 50% so you need to keep your load resistance at least twice the internal impedance to be in a reasonable region.
Now what is the internal impedance of an F & P? I have no idea. With air gap machines into rectifiers the effective resistance seems to work out to about 1.3 times the winding resistance measured between two terminals in star.
Unfortunately that is not going to work with an F & P because it will also have considerable leakage reactance.
What you need to know is its synchronous impedance. A rough way to determine this would be to run it at constant speed and load it with a variable resistor until you reduced the output to 1/2 of the open circuit volts. Normally this would be with a balanced 3 phase load but in your case loading after a bridge rectifier would give an equivalent synchronous impedance referred to the dc line. A strange concept but one that would be relevant to the way you are using it.
If you are prepared to run it as fast as you want, if you load it so as to keep the efficiency up, thermal limits will not apply, it will explode mechanically or more likely break down the winding insulation at the limit. ( I doubt that this limit would be realistic for you to reach that speed from a prop).
When you look at things here don't forget that nearly everything is for direct battery charging with no load matching ( that's just what most people do).
Virtually all commercial engineering for normal alternator uses is for fixed speed balanced 3 phase loading. When you try to do something odd you have to seriously think about where you start chasing information.It may be on the internet ( probably not) but it is up to you to pick what suits your requirements.
Flux
