Motards are the best fun you can have below 80mph! I was reminded how much fun singles are when I got a 690 enduro loan bike, and bought this very recently:
viewtopic.php?f=8&t=15053It's a 520 EXC (with a newer head etc from a 540). It's my first proper motard as I had a street moto before (XT660X, very good bike, but different thing).
I tried my mate's 450 EXC and thought it wasn't grunty enough for the road, but I did just come of the SD, so it was hard to compare.
Saying all that, there's no way I'd swap the SD for an EXC. I love long distance rides as much as the blasts down the local lanes, and it'd be hard to take an EXC on a weeks touring or even a long weekend
So I'd keep the SD and get a cheap-ish EXC as well.
You probably know this, but keep in mind that they are competition bikes, so very regular oil changes (approx 300 miles), filters every 2nd or 3rd oil change and regular engine rebuilds are common. So if you buy one and you don't know the history, expect to have to rebuild it.