I just purchased the 450 last week. I had a z400. It had +2 arms, tripple rates w/rezzy and was a nice handling bike but was lacking in power. It only had a pipe, jets, kn, 13/41, so there was room for improvement but in races up olds it couldn't hang with the banshee's or raptors my friends had.
My friends raptor, with alba pipe, kn, jets, would beat just about anything that wasn't a built 250r, banshee, or raptor. He runs 22 edge tires with 12/44. It was amazing how fast it would go, and really depressing if you know what I mean. Anyway, the last month we have gone twice, and with the introduction of the 450 things have change. These things are wickedly fast. A 450 with pipe, kn, jets, can take him by 3-5 bikes up olds. I never thought that was possible. The banshee's are even farther behind, like 6-9 bikes. If it was only one bike, I would think well they just lied but I have seen at least a dozen that are that fast, it can't be they all have built motors in this short of time. My other friend just got his banshee back, had the heads ported, new carbs, pipes, reeds, it was fast and the hit was hard. There were two 450's that he raced and they both hung with him.
At Hill 5, we call it MF, I think it is the hill past Lizard Slide, I saw a 450 take the hill without paddles, stock dirt, and climb it in 3rd gear. He actually beat two banshee's with paddles. On my z400, if the sand was soft I had to down shift from 3rd to second just to make the hill, if it was worked sand I would carry 3rd.It was amazing. That was the point where I knew I needed one.