Well I know we dont know much of each yet but I currently have a 04 yz450 and absolutly love the power and the 4speed tranny, I do 95% motocross and a little trail riding at my house, the only problem is the bike doesnt turn very well. Any way I am looking at buying another 450 in 06 and I am wishing the new yz was a 4speed which has been great on the track ,dont have to shift too much.I also am wandering if they have found a way to make the thing turn like the other 450s. The new kawasaki 450 is 4 speed and is heard to be great at turning, so I am undecided, although I prefer a more powerful engine and would sacrifice turning ability for it, so the decision is still up in the air. I really wish the yz was 4 speed because that would make it a no brainer for me. rm450 looks good to but dont know if the motor is top power in the class.