I've rode my k5's since 2000.
I have played around with jetting chasing numbers for elevation and temp.
Yes, a bad jetted k5 will still pull away from just about any stock bike out there.
But one that is correctly jetted will rip the guts out and stomp all over them.
In all fairness I couldn't tell a lot of difference on the dirt or sand.
But when I started playing with the street tard jetting became a bit more obvious.