For Ellipsoid HS-81MG is enough, because hard landing should be considered. I don't use Naro because theortically the holding torque for a flying surface depend on 2 factors (speed & surface area). In my opinion metal gear should be used in case of hard landing. If your ships are F3B or 3.6m scale, personally I perfer HS-85MG. Another important factor is precision & speed especilly your ships are F3J/B/F.
(*ps: Sorry I can't write in Chinese via computor)