The first thing I would do is have a PGA pro fit you for the proper shaft.
My personal experience is that the XP shaft hits the ball higher and is better for smooth swingers.
Although I currently play the XP, I took out a old set with the DG shafts recently and they were better for flighting the ball. My Pro suggested going with the KBS tour shaft but I am hardheaded and have always used TT shafts.

TT just released a lighter option w/ the same DG shaft profile... check it out. I play the KBS C-taper Lite in my AP2's.

I had AP2-712s and switched to AP2-716s when they were first released. I have XP90s in the new AP2s. I was fit for the AP2s, but went with XP90s only because they felt the most similar to the XP95s I had in my previous AP2s. My numbers were similar with a couple other options as well. Having played the 716s now for over 200 rounds, I would like to be refit. I have a better swing now and feel I might be able to benefit from something else. Maybe not, but my swing is not the same as it was the last time I got fit. At that time I was about an 11 handicap. As of today, my index is 7.3 and my swing is much better as a result of some extremely good help from my club pro.

I had the XP 90 (R300) shafts in my 716 AP2 Irons for about a year and a half and recently switched them out for XP 105 (S300) shafts. I wanted a lighter shaft than the DG shafts. I am 59 years old and have been fitted at my club at Titleist Demo Days and at Golfsmith (now Golf Galaxy) all with different results. Fitting takes time and is a long process. Use the advice of certified Titleist Fitters and do it outdoors so you can see your ball flight, but you yourself need to decide what feels good to you and how you like the flight of your ball. Try to play a few rounds with different shafts. I took my old 714 AP2 irons and had a local repair guy put one option of shafts in them XP 105 (R300) that I wanted to try and I played with them for a few months before I decided on the XP 105 (S300). Basically, I took the advice of the different fitters and figured it out myself with what I was most comfortable with. The XP 90 (R300) were to light for me at this stage of golf game. Good Luck !

Hi BWright - Playing off 6 - you clearly know what you are doing.
But before you make any purchase - get a Titleist fitter / Pro to look at your swing and he supply you with the best shaft option on the market for your game - and these guys are so good - right on the money. Don't fall into the marketing thing - get the shaft they suggest - i.e. the best numbers.

For me - the best Trackman Data was the Project X 5.5 shaft - and big number changes in everything.

The fitter also suggested the 716 CB Clubs - Dear o dear - seriously take a look at those you will be shocked at how good they are - and compare them to your club of choice.

Hope that helps
M

Great advice from all... very much appreciated! Definitely incorporating all into my purchasing decision as I have very small goal to get to a solid, unshakable 4.