Not to beat the dead horse, but I think you have our answer. I am a 210 46yo vet rider. I picked up a new 2017 KX 450 last year end of season. I was looking for a 250, but I got a screaming deal on the 450, 6K out the door.
Everything people are saying above are true, mostly. I kind of wish I would have spent the extra and got the 250. I do enjoy my 450, but I dont use nearly the power that bike has, not even close. I have whiskey throttled and almost ended up in the woods off the side of the track. I have whiskey throttled it off a double then into the next jump which almost but me into a nasty endo, and I even had a goose fly up and hit my chest on an up jump hill I grabbed a handfull of throttle and was on top of the hill before I knew it and still dont know how I cleared the rest of the hill with out crashing. The 450 has tremendous power and torque. The great thing about the low end torque is you can recover from corning mistakes by just opening (controlled) the throttle. I find myself getting beat up wrestling the bike around.
I have done a few things to my KX to make it more manageable. Kawasaki has 3 ignition couplings, a soft, hard, and standard. The hard coupling takes a little of the hit out of it to try and control traction on a hard pack track. It works slightly, not a huge noticeable difference. The other thing is a Rekluse clutch. Now that made a difference, huge difference. With the auto clutch I can ride in a gear higher which tames the engine braking and obviously takes a little of the steam out of the big hit on the bottom.
The great thing about this bike is I am not abusing the engine at all. I havent hit the rev limiter, knock on wood, yet. Hell I havent been in 5th gear on any of the tracks. So with maintenance the engine should last forever.
Go with the 250F or 2 stroke 250 IMO.
