Never experienced KYB, found koni set on mid settings to work very well with standard springs, never tried eibachs on them.
Bilstein and Eibach seem to work well on the 306.
The spings on mine, i think, are original. However, i think the dampers at 75k are getting tired hence the terrible ride.
The KYB look a great price on Buypartsby. I seem to recall the Bilstein B6's i purchased were much cheaper trade than the retail prices on the web-site.