Had only about 500kms left at the back and the ride was getting progressively worse, add in the fact that I don't like riding a tyre till I can see the carcass, it was the right time.I'm guessing you didn't ride them until they where down to minimum thread depth. Or you just decided to change the tyres a bit early?
I've got maybe 6200 miles which is almost 10000 km and I think I'll still manage about 1000 miles on top. Though 70% of those miles have been done in London so max 50mph (80 kmh).
I have ridden exclusively on road and would not consider myself a nutter by any means.
The Mt60 is just a tyre that uses up quickly.