I just came off the 2006 450, about 2 weeks ago. I have 5 hours on my 2010 not including break-in.
Overall, the bike does fall into ruts much easier than the 2010, it doesnt want to stand up as much, and on flat corners the front end doesn't push near as much as the 06 (if at all)
The 250 engine, coming off of a 450, you will be throughly disappointed with. I borrowed a friends yz250f while he was overseas, put about 25 hours on it, and it needed a piston shortly after. Total of 45 hours on the bike. I feel like I had to work twice as hard to get the 250f to go anywhere. I was racing the 06, which was dyno'd pushing right around 56 rwhp, and the 250 just felt slow.
Now, comparing the 2010's 450 engine vs my 06's 450. I got off the 2010 after a 20 minute session and my first thought was this this is slow. It feels boggy on the bottom, and flat on the top. Im going to change the rear sprocket to a 49 this weekend though. Keep in mind that after putting a couple rides on the 2010, I was turning BETTER LAP TIMES than on the faster 06, so bottom end power and top end over-rev isn't everything.
If you think you want to save the 1700 bucks by getting the 250f, then by all means, save it. But I am willing to bet that you'll put the money back into it with a pipe, several top end rebuilds, and possibly some cams. Where with the 450, you can be content with it out of the box, and if this new 4 valve head holds up anything like the 5 valve head, you wont be looking at a valve adjustment for 30-40 hours, and a piston till 100!
Now thats what I'm Talking about:thumbsup: