FWIW, the big bore I had (KDX240) liked the stock jetting. Even though the engine needs more gas, it draws in more fuel and air with each stroke. That said, I'd go a little richer to start, just in case. Whoever built the engine should have a recommendation for you.
BTW, a cool day at sea level while riding in the sand would probably require richer jetting than any other condition. The bike is working much harder in the sand and generates way more heat, and the oxygen rich air requires more fuel as well. So many riders will richen their jetting when they go to the dunes.