Whether it's true or not (but does make sense to me) is that a 2blader will generally be smoother on a 4cylinder and a 3blader better on a 6cylinder.
The practical theory being that the each blade will be in the same place during the same part of the firing cycle, hence smoother operations respectively.
Speed however, will be more of a function of power provided by area/lifting properties of the blades, irrespective of how many individual blades the prop unit comprises (think of the difference between a 'cruise' vs 'climb' prop on a fixed pitch setup.