Hi Nick, 

Thanks for the question.

When I used to fit individuals into the 712 U, most would stick with the same shaft they used in their other irons. Some individuals would go to a lighter, softer shaft to help increase launch and spin.

Quite honestly, it is really player dependent. My best suggestion would be to see a local fitter and try some different options out. 

Please let me know if you have any questions along the way.

Bubba

When I ordered my 712u 2 iron with a senior shaft, the Titleist rep informed me they could soft step the shaft to make it close to a senior shaft. Great decision...and was please with the input from pro golf club rep. I would recommend you work with your pro club rep for help on what shaft would be the best for you.

Try as many as you can!  My 712u's have true temper xp95's.  I recommend at least try the xp95's if you're able to.  Great shaft.  High launch and mid spin combined with the 712u  workability has been awesome

I second the XP95, I have it in my AP2's as well as my 712U, excellent shaft, great feel.

I have mine with a px 6.0 and love it.  The shaft produces a low penetrating ball flight.