Hi Ellen,

Not sure which KBS shaft you are playing but the shaft comparison table in this link may help: Project X in the middle column and KBS shafts in the right-side column. Please note 'ss' = soft-stepped, 'hs' hard-stepped.

http://www.titleist.com/teamtitleist/team-titleist/f/7/t/19416.aspx

A Titleist fitter did the same thing to me at a fitting. I was hitting the AP2 with DG S300. He said my swing has slowed down a little, and had me try the AP2 with a KBS shaft. Because the KBS is lighter (10grams I believe?) I hit my irons 10 yards further with the KBS shaft. Probably based on your swingspeed, he moved you to a lighter shaft? You should gain distance?

Like you even said, the 712 AP2's are MUCH improved! The longer irons are easier to hit. The short irons are more workable and playable from various lies. They added tungsten in the toe and heel, which provides more consistency (ball speeds/distance control, launch and so on...even with mishits), forgiveness, etc.. They have a much better feel and sound. The improvements of the 712's outweigh the 2008 AP2's very much. The forgiveness and consistency should be enough to consider the 712's. The more consistent you are, and the better you hit the ball, you'll obviously shoot lower scores. 

The 2008 AP2's were great clubs, however, with the newer technology, the 712 AP2's are much better. You WON'T be disappointed. 

If you have any more questions, please, feel free to ask away!

The project X and the KBS Tour aren't even on the same planet as they relate to each other. The spec sheets on the computer may be similar, however these shafts don't perform the same in real world situations. 10 grams between two shafts sounds minimal but it makes a big difference. The project X will load differently than the KBS being that one is a rifled shaft and the other is stepped. You should trust your fitter and make the switch.