Hi i know it depends how you ride but how long would you expect to get out of a set of front pads.I was out to day noticed the lever seemed to be a little further to the bars when applied.
Mine last around 500 miles with all off road riding. Fronts do last longer but I change them anyway. No problem as its a 10 minute job total, to change front and rear.
For me with sintered pads, road/commuter /town bike 1500/2k.
Off road 500/1k, on the south downs it can be 50 miles or less with the
wet abrasive chalky/clag. Front does 70/80% of braking so they usually wear quicker for me.
As above, they are pretty cheap and easy to replace.
I always carry a set with me, but I'm sad.
I have only done a hard 150 miles with lots of steep downhills in muddy conditions and the fronts are looking decidedly thin already after squealing lots its more how they are used and not how far can you get.