IMO 8900 miles is excellent wear on a performance bike. The wear bars are set at 2/32 , so i try to change mine at 3/32. You can probably get another 1000 miles at the most. Not sure about the question of different gauges, but suspect they are the same. As a FYI I only get 6500 to 7000 on my PR4GT mounted on my K1600GTL.