Jesper, I have been trying to get into RF's but the time isn't right. Are you saying that slower lenses have more blades in general or Leica specifically?
20 blades as eSPhotos recommended has piqued my curiosity. Other examples by Thomas for the 85mm Jupiter or Helios too.
Here are a couple of examples that clearly show my interest regarding the different results from a 10 (top) and 7 (bottom) bladed lens . . .