That calculator I posted earlier in the thread will help you a bunch with rates. It also has a chart listed with combinations of rates and the combined initial rate of pairs.
You want 1-2" of preload to get some spring force at full droop. This will effectively make the rebound valving lighter.
If you have less than that preload, you need softer springs, if you have more than that amount of preload, you need heavier springs. 50-100 lbs split between the spring rates is great for getting rid of the body roll as much as doable with the springs.
Get the springs all correct first before doing anything with valving.
Change one thing at a time.
This is all a regurgitation of Wayne's spring theory that works. Seen and experienced it first hand.
The trouble with really light long springs is they start to bow and rub the shock body.
This is why you see people moving towards link mounted shocks with a mechanical disadvantage through the motion ratio.
Moving the shocks would allow you to run a stiffer spring, with correct preload, and keep the same ride height.
I'm not saying you should do that, just posting the knowledge for tech in this thread.
For everyone following along, having preload give you a more linear spring force curve from full bump to full droop.
No preload equates to much more spring force at bump and zero at full droop. This is a pain to tune, and generally results in the suspension packing in. This means the axle can't rebound fast enough between the bumps.
The preload helps to push the axle away in rebound so that there is travel available to soak up the next bump.
Sorry for the long post, just trying to help anyone that comes across this thread while trying to improve their suspension.
Edit:
Here is link to calculator again.
http://metalwerxdesign.com/files/springcalculatorv2.xlsx
