Well I have had the GC Coilovers on my setup long enough now I can make some comments on them now. Note these only are in regards to being a daily driver I haven't been to the AutoX course or track so I cannot comment there...
Recomended String Rates/Lengths
Front 300lbs/inch 7"
Rear 250lbs/inch 7"
If you use these springs and have the collars at the top you can acheive stock ride height
I recommend the use of Koni Yellows I find the KYB GR2's can be somewhat bouncy I assume its due to the high spring rate. Also not if you are using GR2's the strut body is physically smaller than the AGX body (which my kit was built around) A good way to file this space is but cutting a rubber mouse pad to size and wrappring it around the strut body it keeps the collar in place and keeps noise to a minimum...
I am going to do a VFAQ on this ral pictures and the Diaglog on the talon VFAQ is deceiving and I will correct the text to make it more clear (If you read it the way I did you get VERY noisy front coilovers).
Its very firm but not harsh so if you looking to ride on a cloud like you would in a Cadilac or similar vechicle forget it this is NOT for you. But you could drive the car a couple hundred miles get out and not be totally crippled... It seems going over train tracks is very good (with cut bump stops) it doesn't bottom out.
I currently have the fronts on full soft (I just put them on the car recently and have tuned them up yet.)
I currently have the rears set for 1/2 turn from full soft.
I have the fronts at the top of the collars (although I only have 6" springs this nets me about 1" of lowering. Rear collars are set at about 7 threads from the top (7/8" of lowering in the rear) It looks great corners very squarely only a small bit of understeer. Very sporty feel. As for noise from the coilovers there is none (The only time you get noise from coilovers is if you use cheap ones or they are installed in-correctly or have bad rear top hat seals like I had.) I had to buy some replacemnt rear top hats seals and rear sleeves from Tony @ GC and he was more than helpful in getting me all the parts I needed to convert the set from KYB AGX compatible to Koni Yellow (their perces differ there for you need new rear sleeves)
Hope this helps..