I haven't really tested pigment inks very much for fading, I'm afraid it's at least as complex as with dye inks, and
@The Hat is becoming the Myth Buster now..........
The WIR reports show that their performance rating depends very much on the paper used - very similar as with dye inks, but Canon or Epson tell us in their marketing postings that the pigments are sitting on top of the paper coating - so how then can the paper have such an impact onto the overall performance - there must be some more interaction between the coating and the inks with the pigments..
I have just started a new test on how the Canon 56 pigment inks fair against 3rd party pigment inks from OctoInkjet, the Maxify Verses the Pro 10.. One against one..
Canon calls their pigment inks for the Pro1000 etc 'Lucia Pro' inks, a name like Chromalife 100(+) for their dye inks.
Not all dye inks for the Megatank printers are these Chromalife inks - only for the G550/650 so I can easily assume that the pigment inks for some printers are not Lucia Pro inks either.
Epson has two ranges of pigment inks - Ultrachrome HD(X) and Durabrite for desktop printers mainly tuned for use on plain or matte paper as Epson explains it - and yes - the Durabrite black is a matte black , a glossy black is not even available, and the CMY inks show more gloss/bronzing effects than the Ultrachrome inks on glossy papers. But I never tested them for fading.
It's easy to run a fading test with an Inktec dye ink and Inktec pigment inks - they'll perform better than the dye inks but it is just not possible to generalize such finding to cover all the inks of all other suppliers.