Once you get into a shaft line, the torque difference will modify how much "snap" there is to the club head. Based on transition and club head speed, too little torque will have the head rotate too much and result in a wider dispersion pattern. Too much torque and the head will not flex as much, potentially losing some distance and leaving the club head open through contact, tending to a fade. Short of a shaft marked "upcharge" or "exotic", Titleist clubs are the same per club regardless of off the rack, "standard" shaft, or custom - n/c, so it pays to get fit to get the correct shaft in length, weight, and flex for your swing.

Yes Timo, the difference between the AMT stiff and regular is just like the difference between the Dynamic S300 and R300. If you are going to invest in a new set, you really should try to get to a Titleist Thursday, demo day, or somewhere that you can use TrackMan data to help you get the right iron and shaft combo. I went to my fitting sure i would get AP3's and ended up in T-MB's.

As adviced above here get fitted and try them out.

When I started playing a year and a half ago I was told reg is this speed, stiff this, and x stiff this.

Since than I have played senior flex ( box set) to x stiff current driver, and stiff shafts in irons.

I found out all that stuff for me is basicly nonsense. I need a shaft I like the characteristics of i.o.w. I like the bent profile, and the feel that comes of it.
Cause at the end of the day the shaft that feels best will give the best results wether it be a reg, womens flex or XX- stiff. Just try them out and see what fits you.
I really liked the dynamic gold S300 myself. But also the project X LZ 6.0 and 7.0. So yeah. Try them out i’d say.

Good luck on your quest!