Gearing is personal and my experience is lower gearing gives you more punch off the mark. More punch out of corners and more grunt to get that front wheel in the air.
I run 15/48 and find it a good compromise. A few more horses and a six speed box would allow higher gearing and not jeopardise low down pick up.

I haven't done the Simpson but have mates who have and if you're going straight over the dunes the tenner is not the machine. Far too heavy.