Goddamnit Jhill i was just now mentally trying to back out of this argument lol. Now i have to go into thought again about potential material properties and here say theories again
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For one rubber does not and will never hold spring tension like metal. So measuring the cycling rates of one to another is irrelevant, regardless if they hold the same pressure at a given measurement (highly unlikely). But in the case of measuring one steel vs another of fairly similar properties, it is much more likely the cycling rate would remain almost identical if they both are rated and designed for linear force output.
Regards to new versus old. It's also possible you guys felt a difference simply because the old spring has settled into fatigue and spring sag, loosing it's original overall force output. That is not the same as saying two new springs with measurably equal rates will behave different enough to noticeably feel under load.
Similar to worn tires compared to new tires of the same size and model, or even a different model. In most cases we're remembering and comparing the end state of the old vs. the immediate state of the new. This is not a fair analysis and in most cases does not show the whole picture.
I actually have to work today so I'll conclude at this for now and allow you guys to rip into my opinions
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