The curve of the muscle only matters as it relates to how it effects the mass and the weight distribution characteristics. The mass and dimensional characteristics of any iron have to be designed to provide stability, feel and the proper launch dynamics of any given loft. The irons Tiger plays are not an iron most players should even attempt to play. It was designed to fit his eye and provide the performance he wants. He does not require the type of stability that most players (even most other tour players) would and should want from an iron design. Consistency of a design from club to club in the set has everything to do with the mass and dimensional characteristics, no matter the shape of the muscle. We can design highly playable blades with straight muscles or curved muscles. We just have to make sure we have the mass distributed correctly to the shape and dimension of the design.