The real question you should be asking is what spring rate are we running as that would make a difference as to how much pre-load you set. Also, these are really old springs and ones that we've abused. I've noticed over the years that I've had to add a bit more pre-load to get me back to where I was and that's about 3.5" or so of lift. I'm already thinking I may need to replace them with a newer set or maybe ones with a heavier rate.
Ever worry about the coils binding after re-adjusting?