Sorry to meet your question with another question, but have you tried the KBS Tour shaft? I just ordered MB irons with them installed and I absolutely love them!

The same guy who created project x technology years ago started his own company to improve upon it with kbs shafts.  Agree with other post here... You should try other kbs shafts beyond low flight kbs c-taper... Including kbs tour (which many PGA tour players still use), and for a higher loft easier to hit kbs tour 90 more lightweight shaft.  I believe that with the Titleist fitting cart and/or other golf company fitting carts, you can demo all 3 kbs shaft offerings and pick the best feel and ball flight for you.  In my opinion, kbs shafts are next generation project x shafts.... Better feel and energy transfer.

Thanks for the reply. I did try KBS Tour and KBS C-Taper S and X.  KBS Tour only try with monitor.  Feel soft and smooth with quite long distant. But I can't keep it consistency. KBS C-Taper X feel quite hard and not smooth. I have some problem with it too. In the end, I end up with Project PXi 6.0, which kind of balance between PX and KBS C-Taper.

I tried both shafts when I got fit for my AP2 712's and ended up going with the project x 6.5's. I do not regret the decision at all. The dispersion is extremely tight and the shafts feel great in my opinion. I would definitely get fit though, as project x is tricky with their frequencies. My 6 iron SS is about 97mph and the 6.5's work great for me.