Well I'm thinking I'm going to have enough HP to always reach the 3600 RPM, so I'm guessing I might get into using the 18T on the driver.That's a 4.15:1 final ratio with the 54:13, but be sure. If you find you need more low end torque, you may find you need a larger axle sprocket than there is available reasonable ground clearance for it.
Starting with a 10T on the CVT will allow you to use smaller sprockets on the axle, and that can be as small as you dare go to load top end.
Conversely you could fit a real torquey larger axle sprocket without chewing it into the sand. Think wood baseball bat into a meat grinder.