Most players, I believe, will not notice a 100 point playability difference. Ralph would tell you the same thing. However, I think, over time and the more shots that are hit, a player might notice a difference in a MPF of say 455 and 555, one being in a Classic category and the other in the Game Improvement category. Probably more difficult to notice the same 100 point difference between a 825 MPF and a 925 MPF, both being very stable and forgiving.
As far as workability, when talking about left to right or right to left, the idea that a certain design is more workable than another is simply not true when looking at it from a design standpoint. Path and face angle at impact are what creates ball flight and ball flight movement. Assuming the ball is struck on the clubs cg, the ball does not know what kind of design hit it. It just reacts to the angle of the path from which it was struck, the angle of the clubface at impact, and the speed a which it was struck. It is true that if you have a highly stable and forgiving club and you hit it off center, the ball will move less than when comparing to a small blade hit off center. Besides, if we hit the small blade off center the ball may move more, but it will travel much shorter due to it’s lack of stability. However the discussion of a club heads design and it’s effect has to assume a both struck on center. As far as up and down, high or low workability, lower cg irons may require a little more work/technique to keep the ball down than higher cg designs. The only other factor that can effect the ability of a player to maneuver shots with a design is the aesthetic, or appearance of the club. I have known players that say that they feel they can work the ball more because of the way it looks. Generally these would be elite players and the consensus is less offset and more of a “blade” profile, in their mind, makes the club easier to work. Fact is, they can work any club, but to their eye they like to see a certain look.
Hope this helps.