On standard BMW pads,my fronts have never been changed and got the following sort of mileage on my last 2 GS's
1100GS - sold at 36,000 - never changed front pads ABS
1150GS - sold at 24,000 - " " " Non ABS
Current 1150GS - 15000 miles and only 1/3 worn.
Rear pads on 1st 2 gs's were swapped at circa 20,000 miles- ABS