Depending of the brand, brushless motors can be very different gearing-wise, although the winds are the same.
That's why it's not very useful to ask, say, 'gearing for a 6.5' if you don't give the brand, rotor size, sintered or not, etc.
When I first tried a brushless motor (Orion 6.5 with 13mm rotor), I used the conservative recommended gearing. It was so slow!
It's only when I geared it with 4 more teeth on the pinion
that it came to life.