I have had a chance to ride both the EXC350 and EXC500.
Rode the 350 first, Rekluse and LHRB.
That bike is just fun to ride.
It felt and handled just like my 07 XCFW 250, but the power was like the old XCW400.
Nice and mellow down low, get the rpm's up and it moves.
A few weeks later I rode the EXC500.
No Rekluse or LHRB though.
Now that's a bike I would like to own.
It makes my 530 feel like a pig.
I myself don't think that it's too much for tight single track trails.
I like the fact that there is not a lot of 4-stroke engine braking with it.
The owner put a one tooth smaller countershaft sprocket on it, with the addition of a Rekluse that bike would chug anywhere in third gear.
As it is without the Rekluse it had a habit of stalling out when going slow and whacking the throttle on in third gear.
Never had it happen if first or second gear.
The power is so mellow down low in the rpm's.
It has a lot more grunt that the 350 does.
I am amazed by how KTM has made these bikes ride so nice!
Now if I could find someone to buy my 530....