Stuck on shafts

I had a Titleist fitting on Saturday for a new set of irons. I was pretty much going in knowing i either wanted the 712 MB or 712 CB. I tried out the heads for a bit and decided that the MB head was superior for me (picker, pretty accurate ballstriking). I am 16 years old and about 6"1 1/2 and about 135lbs. Right now i am playing an AP1 with regular shafts, and the fitter reccomended i go into a stiff shaft as i grow older my strength and swingspeed will increase. Right now my swingspeed is around mid-high 90s with a driver and around mid 80s with a 6 iron, and only about mid 160s with a 6. He gave me both the DG S300 and the KBS tour in stiff, and decided that i liked the KBS better. I am a natural high ball hitter, i even hit the S300 pretty high. The only dilemma i have is wether i should go for the R+ or the full out stiff in the KBS. I watched a video online about how KBS has a taper system in their shafts that allows people to load and release a higher stiffness shaft, which could be his reasoning behind his reccomendation on the stiff KBS. He also put me on the Mizuno DNA fitting club just to see what would come up, and what came up was the KBS and the dynamic gold but in regular flex. (the mizuno dna club is much heavier than a normal club, im guessing thats the reasoning behind only a 79mph swingspeed on the DNA club).

based on what ive said, do you think i should go for the KBS stiff or the R+?

The S300 seems a little stiff for mid-80's. I swing my 6i in the high 80's and lost a lot of consistency when I swung the DG S300, just because I had to swing harder to load the shaft correctly. I personally really like the KBS Tour stiff and have recently looked at the Project X 5.5 and 6.0, which seemed pretty nice. I'd definitely recommend KBS and Project X, but am hesitant without actually seeing any of the data or your actually swing to encourage you to get the S300.

Another thing to remember is the S300 is sorted by weight, which means the actual stiffness varies from shaft to shaft, whereas the KBS Tour and Project X shafts are sorted by stiffness, where the weight will vary slightly. I think the KBs Tour Stiff. If I remember correctly, the KBS Tour's stiffness is 5.1 for a reg, 6.1 for a stiff, and 7.1 for a x-stiff, while the PRoject X shafts stiffness is in the name.