I've got a 950 with 45k on it and got it with about 18k on it. It's already had all the engine mods and the bulk of Pyndon knowledge put into it. The engine was rebuilt by him after some fuel confusion by the previous owner.
It's had a fairly hard life whilst in my ownership with off road tours of Morocco and competitions in the UK
The only time it's let me down is when the believed to be indestructible facet pump I fitted gave up and I didn't have a spare with me. Swapped back to the KTM one as at least you can normally make it get you home.
I think key thing with these motors is to keep on top of the maintenance, neglect it and you'll pay.
Chassis wise, not much goes wrong, even when heavily abused. Stick with KTM bearings as they seem to last much longer than other makes.
That's what I've learned in two years.