I have the same shaft (KBS TOUR X-Stiff)in my 712U 2 iron as in my irons. I previously had the KBS C-TAPER (same flex) in the 712u but the launch was too low for me (I purchased the iron used and that was the shaft in it). I love the ball flight now.

I would be interested also in the experiences of those that have switched from the 712U to the 716 T-MB!! I have considered making the change...actually have seen a few used at the local PGA Tour Superstore. I like the forged feeling of the 712U as it is the same as the 714 CB/MBs that I play. I have only hit the 716 T-MB inside but I'm looking forward to hitting it outside to get a better feel for the club

I have tried both my current iron shaft (DG X100 SSx1) and a heavyweight graphite. I have to admit the lighter shaft helps a lot!