I have had each generation of the R7. You are correct, it's all about the shaft. The TP shaft has a different kick point and is stiffer.
I switched from the TP Fujikura Speeder shaft to the "TaylorMade RE*AX shaft" and added 20 plus yards. Ball flight is now perfect for my swing speed and path using 9.5 degree loft.
Love this club!
JJ
Atlantic City Golf