I had Schlumpf 152mm cranks on mine until they cracked. I was thinking about moving down a size anyway, and that was the incentive. I went for 127mm Pro Wheel (Qu-Ax) ones, and was amazed with the ease that I got used to them. The shifting seemed to be much more natural, but without ever having an accidental shift. (I only had 1 on the longer cranks, and that was whilst holding on to a railing at a red light).
I had the same Schlumpf frame as you when I swapped for these cranks, and had no problem at all, but this is the same combination that Joe tried and had the problem with the crank and frame rubbing. It might just be an issue with tolerance, but for the cost of a few Euros, is probably worth trying.
STM