Did some more pads testing today, and I can confirm there is an effect on sound. Compared to stock, all three alternates make the bass drier but to a different extent: mesh and velvet just a little bit (I cannot say if there is actually a difference between the two yet), sheepskin quite some more. It's similar to changing the reverberation of the room: less reverberation meaning drier bass.
The most dramatic effect is with orchestral music. I was having troubles listening to it with stock and both the new mesh and velvet: just too much reverberation, causing quite some confusion. Now with sheepskin reverberation is close to perfection and everything can be heard really well. With this record the difference is outstanding and R10D really shines:
On the other hand, I wouldn't recommend sheepskin for piano solo, being it classical, jazz or whatever. Stock is great for it, and alternate mesh and velvet just a little bit better. This is also true for pop, world music, electronic and generic jazz, at least for the few records I have tested so far. In other words, for now I recommend sheepskin only for classical orchestral music, for the rest alternate mesh, velvet and even stock are better.
Regarding mesh, I stress that stock and alternate are almost the same, but alternate are a few millimeters thicker in the thicker side (sides are uneven in all the pads) but not in the other.
YMMV etc.
I'll keep testing...