dvwalker - thanks - I was not aware that a spark arrestor would make any significant difference unless it was clogged. Sounds like the AUS map is the way to go.
calltrex - yes, a second set of wheels is an excellent investment. I have 2 sets of wheels for my 400EXC. My "woods" wheels have rimlocks / Pirelli MT16 rear / Pirelli Scorpion Pro front. I'm running Dunlop D606s w/ no rimlocks on my second set for 50/50 dual-sport.