If you want to, consider the use of a shaft with a parallel tip, not taper. I don't care which brand, as this is very much true for the majority of brands. In the trimming instructions, you will find a directly relevant detailed answer to your question. You will find the instructions for a shaft that comes blank at a combo flex of A-R or R-S or S-X. You will read between the lines that you are to trim the tip to suite the flex you desire. You will read that the range of tip trim causes the flex to move from the lower to the upper range. You will read that this range of trim is 2 inches. This is going to effect feel, or vibration, and you may tune it to suite yourself. They may say reg flex tip is 13 inches stiff is 11 for example. I think I recall that is the TT version. It might be FST (KBS)
If you are like so many people that wish for less stiff long irons to elevate ball flight but stiffer short irons to enhance dispersion, you will read between the lines and see that you may have a 1" trim to acquire a firm flex. You will read between the lines to see that you may trim small increments to have reg/firm or stiff/firm. The key here is that you try all that, Ho some more shafts, try them out, and work it until that ball goes where the hell you think it should.
This grip insanity you have going is a curiosity. I understand grips in the love line for putters, and taking the wrists out etc. I think its stupid (I think the putt is a baby iron swing) but I understand the thinking. Has somebody convinced you that the grips don't go down into the fingers? If your grips aren't down in your fingers and you are palming the grips, doesn't this prevent you from making an acute lag angle at the top of your back swing? You need a flag if you cant go back, cause you have a flagpole sticking straight up. The lag is in the right wrist, but if you stiffen iron grips to follow big putter grip theory, you have big iron putters that fly crazy because you have reduced the two lever action inherent in a golf swing. I wear an extra large cadet glove. Short fingers, get it? I actually jam on undersized shafts. You have to get your Palm Pad on top of the stick and fingers underneath, and the bigger the grip, the more you are gonna cheat that pad to the side. Did you ever consider the choking up you see on the PGA TV? Did you ever wonder why? They are getting a very comfortable handle down lower in the smaller diameter area of the grip.
I currently have oem KBS tour regular shafts in my TM irons. They are 1.8 torque mid bend. You cant get the same flight from the same flex TT DG because the TT are high bend so play them a fraction softer flex to make it up if you wish. The TT DG are also + a little torque compared to the KBS. The single most important thing is YOUR ball flight, so you adjust it accordingly. I know specifically the "Butter" you refer to, and I find mine in the TT DGR400s. I have two sets of DG R400s that I have yet to install, they are my favorite base to trim up from in flex. I think the DG is a smoother feeling shaft upon impact, but I enjoy a mid height flight design.. I can always knock a ball down when I am into the wind, its harder to float it up when the wind is behind me.
The more brittle the steel (1035 steel is 35% carbon and thus less ductile) the more glassy the shaft feels, but the less torque you can have in a similar wall thickness shaft compared to 1025. Its the metal way to do what they do with low torque graphite wood shafts. Same effect, different materials.
Ok long way around to say Torque is Butter. But Better Butter? Thats up to you. On this chart, please dont use the minimum speed. All your "gotta make it" swings arent gonna be as hard as you can swing. I paid 600.00 for the best laser I could find. When I say my normal accurate 5 iron is 170yds, I am not fooling like so many.
I hope some of this helps.