Instead of "effective mass", I like to use the "hitting weight." Interestingly, the simple definition of hitting weight that I use correlates well with Cross's results for "rebound power," even though Cross never seems to make the connection in his papers.
The hitting weight HW = M*(R - 4), with M = static weight in kg, and R = distance to balance point in cm (the 4cm offset is the location where the racquet handle intersects with the extension of the forearm). The hitting weight gives you a very accurate measure of a racquet's power level due to the weight distribution.
If you take any 2 racquets with the same hitting weight, same stiffness, and same tension/stringlength ratio, they will have approximately the same coefficient of restitution.