900 Trail in the Dunes

Just about done with the break-in on my 2015 900 Trail and am wondering what gear you are using in the dunes. It is my understanding that it’s not good to lug the engine in high gear. Is this true? How fast can one run without causing problems in low gear? From past experience with quads wheel spin and speed are a must on steep hills. I’m afraid low gear may be too low. Any advice or experience will be appreciated.
Dick