jdeuel87, Tom is right on the angle mounts, the more angle you have the more spring rate you will need. I change the upper mounting points on my jag rear coil overs and ended up with 27 degrees, after going through three sets of springs, 4/600 lb springs worked for me.
I highly recommend 'PRO SHOCKS', they swapped springs each time at no charge while I worked this out.
http://www.proshocks.com/