Out of the box, it was a little lean in the upper-middle for pump gas. raising the needle 1 position fixed that.
Stock, it's a little dead until you get into the midrange. A PC or Bills pipe makes a HUGE difference. The very bottom is still pretty dead, but it really pumps up the low-to-mid transition and opens the top-end a tad more.
The Rad Valve (and I'm sure the V-Force) greatly improves the responsiveness...RMs always rev extremely fast in neutral but with the reed valve, it carries that quick revving onto the track.
I don't think that the jetting is a bad as some have said. I do tweak the air screw every time I ride. If the temps are really cold in the morning and then warm up, I will move the needle up and down 1 position.
Right now, for fair weather (65*-85*, 1500' asl) I'm at 45 pilot, the clip is in the 2nd groove from the top(stock needle) and I have a 162 main (I could probably go to a 160, but...).
For MX, the suspension does need some work. It's actually really good on everything except on landings. It bottoms out pretty hard.
Oh yeah...get some steel clutch plates and 2003 KX250 fibers when it's time for a new clutch.
Enough info for you?