I would NOT make this switch. Unless you are totally sold on the "Game improvement" marketing aspect of todays manufacturers, stick with the CB's.  There is no need to spend 1100 on AP2's when you can take that $$ and get a few good lessons and improve your game by 2 shots a side.

Jack always had multiple sets of clubs and he was successful with every set he owned. If you can hit a ball, you can use any club. As an 8 HDCP, you should be close to breaking 80, so lessons would go much further than a  new set of clubs.  I play to an 8 HDCP as well and have broken 80 with a set of blades. With my "GI" irons, I have never brioken 80

I agree with Tim.  No reason to spend $1100 on a new set of irons.  If you are an 8 handicap, most likely the issue with your game isn't hitting irons.  The 3 "scoring" clubs are driver, wedges and putter.

Have to analyze what you hit well and what you don't hit well. 

1.  How is your short game?  Most of the shots in Golf are taken under 100 yards.

2.  How accurate is your driving?

In addition to the great questions posted -

Do you have any issues with trajectory on any of the 3/4/5/6 irons?  You could just add a couple of AP2s and keep the CBs for the shorter irons.  This is a fairly common mixed set.

Agreed.

Also could try a 21H or 21F alongside the 3 iron to see what you like better. 

For that matter analyze how you hit a 3 wood and maybe consider replacing it and the 5 wood with a 4 wood (17*).  

i have a 21* 3 hybrid to replace my 3 iron. what do you all think of trying a 712u to replace my 4 then keeping 5-9 cb

played today. shot 83 at the number 2 ranked course in tennessee with 4 double bogies... very frustrating

If you are having ball striking/directional issues with the 4CB, you'd probably like a 24H more.  It will tend to have a higher flight launch and stop better than a 4I. The 712U would be more penetrating and could be more useful if you live in Dallas or west and have that constant wind issue.

Zip down to the pro shop,and have a hit with an Ap2 . I had a set of 710MB until I tried the Ap2. I usually hit my MB 7 iron around the 155-165 mtr mark but with the Ap2 I hit them further as they are a higher loft club with the tungsten weights. I have knocked 2 stroke off my 8 handicap,in the last month. I agree that it's alot of money but if you sell your clubs, make a day 3-4 times a week to go hit 100 balls your handicap will drop. My decision to change was the feel of the club in my hands.

Good luck with what ever decision you make 

Hi, the best way to find out if you're playing the best irons and shaft to fit your game is through a fitting session.

Before making any switch pay a visit to a Titleist authorized fitting center or facility. I went last year to Acushnet in MA and had a wonderful time and learned a lot from and for my game.

Now my game is more consistent and the best switch i made was my iron shafts and wedge set-up. Ball selection is also a key.

I play to a 2-3 hdcp and sub-par rounds are more common than before.