Well the reason I said 75MHz is that is what is used in the USA for ground RC. The other frequencies you list would work better than 2.4GHz due to the fact that they are not line of site protocols, are nor susceptible to signal reflection issues found with the 2.4GHz frequencies from water. It's a much longer wave length and can go around hills and not be bothered by water reflections of transmitted signals.
Good luck on your quest.....