How much pavement will you be riding? I'd be inclined to still run a 606 on the back. That's the end of the rainy season in the SW and you might just see a little mud
Hate to tackle that on 50/50 tire with a loaded DS bike. Personally I prefer to trade off some street manners for dirtability
when it comes to tires, esp if I'm in the middle of nowhere. Sounds like a great trip!