DonM, I was on Mizuno MP67 with DG S300 shafts before my shoulder went crap, and was still trying to use them after op/rehab. It was clear they weren't working for me so had a Trackman fitting session with my club pro, tried Mizuno JPX919 and new Srixon range, not much better.
Tried Taylor Made Sim Max OS , KBS (Max?) 85 in regular. Swing speed went up 5mph within a couple of swings and distance (Trackman) by 15 yards. Very fast off the clubface (for me), good launch angle and spin rates I can live with.
I've got a few rounds in with them now and, while still getting used to them and ironing out my inconsistencies - partly down to not being able to play regularly if at all - they're a world apart for me from the MP67s.
I never imagined using "old man's cheat sticks" but when pain, injury, and/or aging took most of the fun out of golf something had to give.