David,
I truly envy you!! Nothing makes a golfer happier than the undivided attention of a pro/fitter and all the latest kit to play with.
I changed from 712 AP2's to 718 AP3 5/6/7 & AP2 8/9/PW in April. I kept my 716 T-MB 3 & 4 irons at the top end of the irons. I felt that the 712's "plateaued" at 5 & 6 and the distances achieved were too similar so I went for a combo set.
Got KBS Red steel shafts across the 718's.
I'm really pleased with the outcome. Gapping distances are consistent and I'm very impressed with the 5 iron, which really goes the distance. Would have bagged the AP3 4 iron in other circumstances.
In prep'ing for the fitting, consider the distances you want to cover off and work from there.
I didn't think there was much price differential between AP2 & AP3 so it comes down to feel, choice & fancy.
I suddenly found I needed irons 2degree flat this time - Shows the benefit of a good fitter!!
You might want to consider the PW, which has a stronger loft than earlier versions. There is an AP2 Gap Wedge available, but it's dearer than a Vokey SM7. I ended up with a 50degree SM7 to maintain gapping.

Lots of decisions in a short space of time!!

Enjoy.

JT

Thanks for the feedback JT, I hadn't really considered the options of going for a combo set, having played with forged irons over the years I prefer to softer feel, but maybe a trade off that would suit if I went for a the AP3's in the longer irons. We shall see what the fitter suggests?
thanks again!
David