A +4 swinger works good for dune riding.  I rode my hybrid on a factory swinger making 68hp and it was too much in the dunes.  The thing would wheelie without effort.  It's now at 74hp with a +4 swinger.  The +4 made it way more controllable and a little smoother of a ride.  The +2+1 arms are also a good idea for the dunes.  That little bit of extra width makes a huge difference in stability at speed while turning.

You running a wider axle in the rear as well?Or wider A Arms with stock width axle?