With differing grips the cpm’s of a club can maybe differ by about 6. Probably more than stepping the shaft.
Will the club play differently, or is it just a question of feel in the hands. ?
First, it is important to understand that although different types of sizes of grips can influence how a frequency machine reads the oscillation, the shafts stiffness is not altered by the grip. The frequency Machines readings may change based on the grip, but the shaft does not change flex. When I build my clubs and use the frequency machine, I use the reading without a grip installed to insure I have the proper progression and that there is no grip influence. Many frequency charts are based on numbers for “gripped” clubs, but this can be deceiving, for the reason you mentioned – different sizes and styles of grips can cause the frequency readings to be different. The reason is the way grips affect the clamping pressure.
The type and size of grip you play can influence performance, but it is mostly based on how you react to the feel of the grip type and the size of the grip on the club. It is long been thought that if a grip is too big, the tendency is for shots to go to the right (for a right handed player) and if they are too small, the shot might tend to hook or go left. The truth is, if the grips do not fit, your shots can be inconsistent, but not necessarily consistently off in one direction. Focus on getting the size and style of grip that allows you to grip the club with the proper grip pressure, which should provide you with comfort, security and confidence to execute your best swing.