I asked the company about that, they responded immediately (cool), and here's what they steered me to:
G2 Throttle Tamer for Dirt Bikes
Make
Yamaha
Models
YZF250-450 (1998 & newer)
40-4Y-HYK-YZF 1
The hills out there are fun! Deceptive, too, because they look pretty straightforward, but you get halfway up, and the rear tire wants to spin or dig, it's not sure which. Unexpected course changes are frequent as you try to maintain forward momentum. "Crap, I'm gonna hit the rock! Crap, I'm gonna hit the other rock!"
The WR's mix of reasonable weight and high rpm power are just about what that surface needs, it seems.