This is slightly off topic, but as the topic is regarding pads, I shall post this up.
Coust pads and Coustsink pads use the exact same material. The possible reasons for different performance from the same material can be down to how the material is cut and how each pad is fitted to the backings as Azarathal has mentioned.
I have been emailed by steve Spurgeon (Heatsink Bikes) a quote from Michel Coustellier.
"I supply with the green rubber to Heatsinkbikes for years for the manufacturing of pads Heatsinkbikes Coust. This material is the same that that used for pads Coust. If pilots have a doubt, they can contact me directly on my e-mail to have the confirmation of it.COUSTELLIER Michel"
I would like to think that this will finally clear this confusion up.
As for which pads are best, all pads are going to perform differently based upon the riders brake set up, (with or without a booster), also if the wheel is ground, if so how harsh the grind is, Even the frame can have an effect on the brake performance, a flexy frame may cause a set of brake pads to perform differently to the same pads on a stiffer frame.
I have used the Coust pads and the Heatsink yellows in Heatsink CNC backings. Both pads in my opinion worked briiliantly on my set ups. I am currently using Coustsinks (but I have the material fitted to TNN Belaey backings, just a choice of mine), which again in my opinion are working as well as my Coust pads, in fact I feel they are holding a bit better, but that could be down to a different frame and brake set up. Both Coust pads and Coustsinks were fitted on pretty much dead grinds and almost straight away were working spot on.
I have also used the TNN Belaeys which I found worked really well, though the performance seemed to drop after the pads had worn about half way.