Right now I have an '03 YZ250F and it's been a GREAT bike. I'll be getting a new bike this year and was pretty much sold on the new YZ250F, but now the 450F is looking tempting. When I got my 250F, I was riding about 90% motocross and 10% desert. I got this thing coming off an RM125. I love how I have so much control over the 250F. It does anything I want it to do whenever I want it to do it. My friends all said that I rode the best they've seen on the 250F. The power is great too. I honestly have never really needed anything more except in the desert and in Baja. I'm 6'1" and 165lbs. and the ergos on the 250F fit me well. The suspension's great, I love the handling, and I pretty much swore by the 250F. Taking the fourstroke out to the desert opened up a whole new world of riding. I love desert riding now have been riding about 75% desert now. I just did a three day trip down in Baja, and ever since the 450 has been looking like more of an option. The only thing I'm worried about is the 450 being too gnarly, wearing me out, and taking the fun factor away. I can ride my 250F ALLLL day. I've ridden a YZ400, a YZ and WR426, and a '03 YZ450. I honestly think I liked the power delivery of the 400 the best. The '03 450 actually kinda scared me. I did about 2 laps around Glen Helen on it and gave it back. The motor was SOOO gnarly and the bike felt heavy and it bucked me around alot. I rode my friends '04 CRF450 and that bike still felt like a big bike, but was alot more manageable. It still wore me out pretty fast though. I'm hoping the new '06 YZ will be alittle easier to ride, I guess they've smoothed out the motor alot. I almost wish they made a YZ350F or something. The extra grunt of the 450 would be really nice to have in the desert though. Just endless power. I'll probably even do some trips to the dunes on it. I'm scared of blowing up the 250F in the dunes. I also want to do some more Baja rides, that was incredible. I want something that I can do anything with, I'll have to keep this bike for at least a couple years. Reliability is a huge factor (which the YZ has proven to me in Baja). Price is also a factor but I'd be willing to spend the extra $1000 on the 450 if I will be happier with it. Anybody out there come off a 250F to a 450F? What are your thoughts?