I run a Karoo front on my dirt rim (21x1.60) and a Heidenau on my 21x2.15 for fronts. I keep a 908 rear around but am in love with my rear Mefo Super Explorer. 908 rear I can only get about 900k, but the Mefo is around 8000K with the same riding. Basically the longevity of the Heidenau rear but more aggressive. It's apparently made in the same factory as the Heidenau's.
I'm on a 2011 990 Adventure that has 15000K on her.