No don't panic, things are not that bad. N50 probably manages 13kgauss in a closed circuit but N45 is over 12kg. At the working point in a gap you will be about half Br so you are going from 6400 gauss to 6500 gauss so no big difference, In reality the difference between N45 and N50 is tiny. The only difference it will make is that you will reach cut in a little earlier and you will run a little bit slower all the way up the wind speed range. This will most likely get you running more into stall and you will have less output for most of the wind speed range so the risk of burn out is actually likely to be less unless you do something to compensate for the stall.
Going from something like N35 to N50 would be much more significant and a winding for n35 would stall badly with N50. To overcome this you could wind with less turns and have the ability to use thicker wire with a higher current rating. You can gain power with better grades of magnet but not without design changes.
Given lots of information and lots of experience you can calculate fairly accurately the current into a battery at a given speed. What is far less easy is calculating temperature rise and the likelihood of burn out. Cooling depends on too many factors.
Even if you measure temperature rise on bench tests you still have no real idea how much better the cooling is under wind conditions and the duty cycle of rated power under wind conditions changes from day to day as well as from site to site.
Flux
