First off, I appreciate the good word!
There's not a huge difference (material-wise) in the different FF materials. As far as I know, they all use Dyneema for the main material, with some adding a smaller amount of another material (usually Vectran). Dynaflight '97 is 100% Dyneema, 8125 is 92% Dyneema, 450+ is 70/30 Dyneema/Vetran, 452X is 67/33 Dyneema/Vectran, etc. etc. etc. Vectran is added to further reduce stretch/creep, but Dyneema has very little to begin with.
Which one is quieter/works better just depends--how the string is made, the number of strands, what the bow "likes", your personal perception, etc.
A well made string from the worst material may perform better than a poorly made string from the best material. Some strings on some bows may be quieter with a certain number of strands, and it's not always quieter with more strands. Some bows will, for whatever reason, be quieter, even faster, with one material vs. the other--I have no idea why it works that way, but it does. Finally, a string that is very quiet to me may be loud to you, depending on your hearing--some folks pick up more on higher pitches, some on lower.
The fastest string is going to be the lightest--fewer strands or smaller diameter material, shorter serving, smaller sized serving--but may not be the quietest, or most stable for you. One trick passed on to me from Rod Jenkins is use a smaller serving and build your nock point up with dental floss rather than add the extra weight of a large serving, or double-serving, or adding strands under the serving. I haven't tried that yet, but it works for him.
Personally, I like 12-14 strands of Dynaflight '97, because that seems to work best for me. 8125 runs a close second, same strand count. The only way to know for sure what is going to work best for you on your bow is try different strings. Since Bob Morrison sends out 14 strand 8125 strings on his bows, my guess is that's what he's had the best results with. I don't make strings for Bob anymore--A&H has been keeping me pretty dang busy for the last good while--but as far as I know he still prefers 8125. A&H sends out Dynaflight '97 (12 strands, 18 in the loops). Padding the loops out to 16-18 strands (with dacron) seems to help quieten the string without hurting performance.
You'll probably have to keep filing the nocks on the GT's. Reason being is those nocks were designed for compound shooters using a release aid--a hard snap so they won't fall off the string. Use a serving size that fits the throat is going to give you a harder snap that I like; using a size that gives you a light snap is going to be pretty loose in the throat.
If you have specific questions about BCY products, Ray Brown at BCY has always been great to respond to my e-mails; or I'll help if I can.
Chad