Spring rate and preload question

I'm trying to figure out which springs I want with the 6112s for my 3rd gen. Reportedly, the stock coil is 700 lb.

Do I understand preload correctly?
During compression;
-a 600 lb spring with 7/8" of preload has 525 lbs of pre-load; requiring 1,125 lbs of force to compress the spring the first 1", 1,725 lbs for 2", 2,325 for 3"...
-a 700 lb spring with 0" of preload would require 700 lbs of force to compress the first 1", 1,400 lbs for 2", 2,100 lbs for 3"...
-a 650 lb spring with 1/8" of preload would require 731.25 lbs of force to compress the first 1", 1,381.25 for 2", 2,031.25 lbs for 3"...