I play the Project X Steel 6.5 in my 712 CB irons. Irons are 1/2 inch longer than standard and 2 degrees stronger.
I love the feel and results. The ball seems to leave the face aggressively (like a mad hornet). Trajectory and distance are great as well.
What shaft would give me a similar feel, mid traj. , tight dispersion and distance in a 913 D3?