Here's a link to one of the original threads that kinda got it all going...
Clutch pedal too soft/no feel? Remove the helper spring!
Any way in short best way to describe it.
OEM spring: has a very non-responsive loose mushy feel to it, it is to easy to push in (I was coming from a 300zx with an aftermarket clutch so as soon as I bought I noticed it was off a lil). This is caused by the spring having a high compression rate.
72577 spring: has lighter compression rate making it harder to push in giving you more feel from the pressure plates. Making it more responsive, you might have to try harder to push it in but it is 100x easier to find that sweet spot with a lil more feedback!
Hope that helps, I'll post and PM this.