Are you buying the blocks used? Because it says in the manual for the blocks that they come with
thermal pads.
Having said that, it does have the right thickness for the most parts (0.5 mm), but how well it
actually performs is impossible to say without having a review on it. It might be great, it might
be crap.
One thing though: I am very doubtful about stacking several layers of thermal pads on top of
each other for going to bigger thicknesses as recommended on the eBay site. The thermal
interface between the different layers might not be as good as if you have one thick pad in one
piece. It might be that it's not as bad since the pads might be pressed into each other and over
time combine into one piece (since they are rather soft this could be possible, though I am
very skeptical).
Personally, I would buy pads of the correct thickness (so, both 0.5 mm and 1.0 mm for the 7970
block, only 0.5 mm for the 7950 block according to the manuals).
