DISCLAIMERS: a) I am NOT a spring engineer (or an engineer of any type), b) I own both Springco and SSS/Tubbs CS springs (in fact I have owned every spring used in the video aside from the Springco Orange and the Tubbs .308/42 coil springs), c) I am FULLY aware that David Tubbs is an advocate of his own products, so spare me the commentary on that. I get it.
Here is a video where David Tubbs uses a pressure sensor installed at the rear of a carbine receiver extension which has been fluted and he tests the following springs for pressure at both installed height (in battery) and compressed (bolt lock-back) positions. You can also see the springs oscillate as they return to battery (though I'm not sure this has any actual bearing on reliability or longevity).
https://www.youtube.com/watch?v=8fMVZbrnvu8
It seems to verify that the WHITE is Springco's best offering for CAR REs.
David tests the spring in the following order:
Worn CAR spring of unknown manufacture
New CAR spring of unknown manufacture
Tubbs/SSS AR15 CS Flatwire spring
Springco WHITE CS spring
Springco RED CS spring
Springco ORANGE (.308) CS spring
Tubbs/SSS .308 CS Flatwire spring
It's an interesting video, all in all.