https://www.pirate4x4.com/threads/the-coilover-bible-part-1-by-billavista-pirate4x4x-com.2702748/
Scroll down to "spring theory" (or read it all if you're bored, it's interesting stuff). Written for coilovers, but the first part is valid for all springs.
I still think your previous (probably gas-filled) shocks added enough spring rate to mask that your springs are too soft. If you haven't noticed the vehicle sagging, then I doubt the spring rate has changed. And as the linked article says, spring shouldn't just change their properties under normal conditions.