compare kdx to xr 650..

I can compare a little bit for you. I have a Suz DR650 and kdx200. After riding both off-road, I can say that I probably will never trail ride the 650 again. The weight is the biggest issue and in my case that is a 100lb difference. In slow speed technical stuff, the weight off the 650 can be a handful and can very easily put me down and getting back up is not easy either. The "flickability" of the kdx is awesome and the front wheel can be lifted with the slightest throttle. That being said, there is nothing that compares to the torque of a big bore 4 stroke and compression breaking of the 4 stroke. Even Scott Summers has stepped down to a 400. If tight technical rocky rooted trails are your thing I would go kdx.

putting a pipe and opening the air box will . :)

One is a nimble weapon in the woods.
One is beheamoth made to go fast in the open.

Scott Summers could ride a 1000lb steam driven tractor and still beat most people.

Both good bikes, but for completely different reasons.

The biggest difference would be weight. the 650 is a tank.

You can pump heaps of power out of a kdx if you do the right mods.

Which bike you buy depends on several different factors.
Where you ride/ your size & weight/ experience/ and good ol' personal prefference.

The KDX is great for woods work. And more suited for smaller people (like 200lbs or less).
If you like nimble bikes that you can flick around a trail, and even a MX track (ive seen some KDX's do VERY well there) the KDX is the bike to have.

If, on the other hand, you wanna twist the throttle and not have to intercom "Scottie" for more warp power.
The 650R is more your bag.
I weigh about 250 and "flickable" hasnt been in my dictionary for a long time. :laugh:
(i ride open desert & singletrack in NM.)
For a bike as big as it is though, the 650 will suprize you in tight quarters.
A KDX will nuke it in the woods of course, but it is better than many people realize. One of those things that ya gotta try it to believe it i guess. :thumb: