spring help!

i have a 91 z28 that i outfitted with a artmorrison coilover kit. the stock spring rate of my vehicle with a separate spring and strut configuration is roughly 550lbs.

the art morrsion kit included a 250lb spring that is 10" heightx 3" id. this spring leaves me with no adjustment down...only up and it's stiff.

i used a eibach ers coilover spring that is 10" x 3" id with a spring rating of 150lbs and it gave me perfect adjustment but it's too soft. the spring bottoms out on itself.

eibach only offers 100,150,200,250 lbs spring rates for this spring size.

how do i figure out what is right for me?

doesn't anyone have a general suggestion or some explanation on the how to equate a coilover spring rate to a stand alone spring?

Not me!!!!SAM!!!

well since the 250 is too stiff and the 150 is too soft i guess i have no choice since i can only seem to find 200 as an alternative. it's sink or swim time....if anyone ends up with a suggestion please let me know.

:)