i've got 8kg/mm fr and 6 kg/mm rear. The car is really stiff - dampening is set @ 10f 16 rear. anything over 100k and you can't really feel it - the car floats. over small dips and bumps however - you'll be jolting like a mofo. i highly recommend this setup if performance rates highly above comfort - my car handles like it's on rails right now - keep in mind though, i've just fully stripped my interior so i could scrape off all the sound deadening material - i know i'm a freak!
PS:10kg/mm is definately too stiff - i'm 19 and crazy, and i even think it's too stiff!