Trying to determine load carrying capacity via a measurement of spring coil winding diameter, length, winding count or wire diameter and not knowing the metallurgy or tensile strength (and other considerations) makes for a difficult to impossible comparison process of the spring's load carrying capacities or expected ride quality.
Assuming we have a constant rate spring, good test would be to load the individual spring unit with a known weight value and record the difference between the unloaded spring height vs. loaded height (preferably several inches, as the accuracy improves with distance). This dimensional distortion can be conveyed as the "spring rate", the spring's unique load carrying value, for comparison.
With a progressive rate spring it will be necessary to load the spring, establishing specific reference points throughout it's as installed and applicable travel distances in order to realize the experienced varying "spring rate". Scott.