if you don't care about riding a narrower 39-40mm rim in the back, have a look at the spank stiffee or alex DX 32 or planet X BMF which is the same as an alex DX32. I have two BMF rims at home, i haven't mounted them together as a set of wheels but i heared they hold a grind much better than try all (i have this on my bike at the moment and i must say the grind vanishes rapidely!!). cheers.