GSP, iv only had the 200 out on 2 rides yet, but the first thing I noticed was how much smoother the engine is, it just has torque, it will happily lug around in 3rd and 4th wheras I found the 125 would not do this as obligingly as the 200.
Chassis wise, the 200 feels exactly the same as the 125, even though the legs it doesnt feel any fatter, and I still have the 125 and have done back to back rides in my backyard.
The suspension is just as predictable as on the 125, tracks over roots and uneven ground very well.
It feels nearly as flickable, maybe not quite as much as the 125 due to slightly more mass and inertia, but still extremely maneuverable.
I only weigh ~140lbs, so the engine differences were pretty obvious.
But the overall difference between the bikes would be that the 200 is just easier to ride, less effort to ride at the same pace, with no noticeable difference in agility. Hope that answers some of your questions.
As for the enduro, I finished 4th in the intermediate 0-200 two stroke class on saturday.
Heres a video of one of the terrain tests, this isnt me riding, but the winner Chris Birch, the same Chris who won the roof of africa, twice
http://www.youtube.com/watch?v=9AmyQaVJOjA&feature=player_embedded