Give Ground Control a call and you will have a suspension package sorted out in no time. They are experts and several of them race E30s. What you need is their coilover conversion with SA Konis. Don't let the adjustability scare you, there is no downside. Also get a good front bar (ireland) and lose the rear one. With their help, you'll get spring rates that will give you great control on track and good ride on the street.
One big reason to go coilover is when I was trying various progressive springs and I never found a setup which gave the car good balance. It always ended up with the ass up in the air and had waaay too much forward weight transfer. With coilovers you can balance it - and I don't even mean corner balancing with scales but just visually setting the car flat.