Dunno. Hex values of 2 and 3 also work.
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Actually, while 2 does add "Clock Frequency Settings" it also removes "Additional Direct3D Settings" from under "Performance & Quality Settings".
Alas there is muy disinformation about the "Coolbits" DWORD and general confusion with various downloads which include other registry entries and schtuff.
A quick goggle produced one claim that ffffffff adds (or unhides) more panels and 3 just the CFS however I have some other panels and options unhidden and they do not seem to have been hidden with 3 again after a cursory check.
I suppose it would be easier to sort out starting with a "clean" driver install, add 3 to see what is revealed then change to ffffffff and check again for any difference.