scotts33 Rick---I have experience with KBS, FST etal. Take your NF2 reading on preferred OG FST 115 and correlate that to the KBS 90. Build one test iron and test. KBS 90 will be softer tip stiffness to the OG FST 115. Unsure if this will be what you seek as you disliked Nippon 950's, FST Pro 115's both softer tip.
Scott, that it what I did to determine the tip trim for the KBS Tour 90 shafts I got. My numbers on my NF2 matched the preferred number for an OS FST 115 Sr. flex 8 iron. The numbers are the same but the shaft doesn't feel the same, at least in the Vertex SL heads. I really think they play stiffer than FST 115. They are listed as R flex and I am trimming the FST for Sr. flex now. I reshafted my old set of Acers this summer with the FST 115 at trim chart for Sr. and they feel perfect and play very nice, but as I posted elsewhere they now give me a yardage gap by not being able to hit them as far. I wanted to put the FST 115's back in the Powerplay Adrenalines and some Sooolong Powerbars but doesn't look like it will happen this season with Mr. Frosty looking down on us now.