The 07-11 WR450 tranny has different internals with the tranny. It is more than just adding a 13t sprocket. That gap b/t 2nd and 3rd is gone too.
I rarely use 1st. Do all my slow tech stuff in 2nd. Power is smoother and more controllable that way. Never had issue with the clutch modulation on either my 06 or 09.
Thought it was a smooth solid clutch.
It can be buzzy at 55mph, but it wasn't designed to cruise at 55mph. When I ride DS, I'm in no hurry, so I keep it around 45mph.
I would take a 6th gear though, but it isn't a deal breaker to me. Maybe if I rode where you ride, and you rode where I ride, we would understand each other better!