I don't think it's a matter of how soft it is, but the outer coating, polish and age of the ball. It also depends on the set it's matched with. Say you have a used set of balls, you buy a new measles, now the cueball is newer and less worn, it will react a bit "heavier" with less draw action, acting like a mud ball would with it's extra weight compared to the rest of the set. Most of the red dot cueballs have been bought with the set and have been worn down along with the rest of the balls.
The only set I found to really play harder or "heavier" is the Tournament set, and that is out of trying probably every known set of commonly used balls out there. I also think the Centennial set plays a bit harder than the Armaith setups up to the Tournament edition but that may be due to the fact every Centennial set I can remember using was well used so the smoothness and polish of the balls was not great.
