Thanks for the helpful replies. Glad to hear loser101's satisfied with the GKs, that gives me some confidence.
FDF vs. the GK drift&grip knuckles seem very comparable. Both offer the same roll center correction and 25% quicker steering ratio.
I really like the idea of quicker steering, but want to avoid any pitfalls associated with sacrificing Ackerman. Sounds like that's not a big deal though, from the consensus around here.
As PoorMans180sx mentioned, FDF supplies 12* Ackerman angle. GKTech's
infographic promises "+5* over stock", whatever that is.
Does anyone know what stock Ackerman is on an S13?
I tend to have a tough time making decisions until I'm confident I have all the data available. But PoorMan makes a good point, at the end of the day I'll need to just pick something and run with it.