I have a 690 kitted with a rally raid, and a 350 excf. I could not imagine a better combo. My best friend has a 450 exc, and we swap all the time. His bike has more low end, but they seem to be almost identical on the top end. We have the same gearing btw. Once I got my 350 dialed, I wouldn't give it up for anything. I turns much faster and feels much lighter than the 450. I have a 3.5 gallon tank and almost always have more fuel than my buddies stocker and we both agree my bike is more flick able.
It does have a more complicated valve adjustment, but it makes the bike feel so smooth while revving. I can't imagine you would regret it.
08' KTM 690 Adventure (RallyRaid)
12' KTM 350 EXC-F
1975 Norton Commando 850 (Resto Project)