just read through this old thread, wanted to add a comment...for the woods, it seems like they need to make about a 375 four stroke, for my tastes anyway.
I can ride a 250f pretty fast compared to most other bikes, you can just crank the throttle coming out of corners and they are so smooth and predictable. But the down side is, I am bored riding the bike. There is no arm-yanking sudden burst of power. There is no extra reserve power to be unleashed when you come to that run-it-through-the-gears, open area on the trails.
The 450 has plenty of power, everywhere, but this makes it tough to finesse through tight woods, lots of clutch work to prevent killing it and then on some of them you get overheating. On a 250 or 500 2t you can ride up a gear (out of the powerband) in tight situations, that's hard to do on a 450....either it's making a bunch of power or if you go lower rpm the chain starts clacking and you risk the dreaded "four stroke flame out".