I have done a bit of stuffing around with both the Pferd files.
Classic has a lower spiral rate and different teeth. Cuts faster, leaves a slightly rougher finish.
Premium is similar to the Vallorbe's in cut feel, speed and quality. Both the Pferd run slightly small (0.1mm) than there stated size.
Overall it makes little to no practical difference. I like the feel of the premium's and the Vallorbe's but the cut speed of the Pferd classic suits people using them in file guides like 2 in 1's
If you have Stihl files, look at the marking. If it says made in Switzerland, they were made by vallorbe. If they are stamped made in Germany, they were made by Pferd