I have been riding a 2007 250f in vet-junior and 40+ for a couple of years now. Because almost all of my competition is on 450fs I have had to learn how to ride harder through the whoops and really learn to carry alot of speed through corners. I do ultimately lose too much on tracks with long high-speed stretches or ( like at my local track) a wicked uphill with a step-up at the beginning. Today was my first try on a buddies 2006 yz450f. Oh-my-freakin'-god! If that isn't like riding a cadillac with a rocket engine, then...then..well you get it. I mean holy-crap I knocked off 15 seconds on my 2nd lap around. Plus I never even felt a slight bit fatigued. Oh yeah...I was so worried-about the dreaded power that I wasn't even grabbin' much throttle. Just riding clean. Ever so easy. I am sold. I was gonna put a 290 Athena kit on my 250f before arenacross starts. But now I am going to look for a recent year model 450f. I don't even care if it is FI or not. I love the suspension on the bigger bike. I am 170lbs and that does seem to be the limit on my 250f. I think my years on my 250f may have helped me develop better habits. Now I think I am ready for the big-boy's bike.