I just get my mechanic to change them and don't wait till they are stuffed before I change them. Any wear means the brakes don't work as well and you may need them one day. They are certainly not expensive to replace and 4 sets for 107,000km is not much really.You definitely use your brakes A LOT!!! What is your preferred brand for replacement pads?
25,000km/set is pretty average. I hardly use the brakes if simply country road riding but use them a lot commuting. I also took the Diavel to the track every chance I got when I was clocking up big km and you certainly needed brakes coming into a tight right hander after the downhill straight.