I've got about 2 hours on my bike now so I have a more clear impression of it. I have a tight little woods course on the other side of our creek that I've been pounding laps on plus some easy riding around the main part of our acerage.
This is no MX bike. As other's have said, it's a bit slower revving than the 400, which does make sense given the longer stroke. It seems to have a bit more torque, though. The front wheel comes up a little bit easier/faster. The engine change is nothing dramatic compared to my 01 400EXC, though. Sort of like a pipe difference in a 2 stroke. I have not had it WFO yet so there may be some difference there I haven't seen yet.
I played with the air/fuel screw from 1 to 2 out. I'm running the OCEMN needle in the middle with a 172mj, same as the 400. It liked 1 out best as far as throttle response. Starting is not as consistent as the 400 was. Any tiny blip of the throttle will make this one crank for a while. On the 400, it still started quickly. Maybe this will get better but it was never a problem with the 400. Might just be learning curve, too.
Turning and cornering speed seemed about the same to me. I'm not sure why but I was able to put in a lot of laps before I got tired. Makes me wonder if this bike is just a little easier to ride fast. Time will tell.
Suspension seems good but my woods course is pretty smooth, too. Some breaking bumps that it sucked up well and one 20" log nothing sucks up well.
Hoping to really ring it out this weekend, especially the suspension, at a rougher single track area. That will really help me know where things are at.