Ilford Prestige Smooth Hi Gloss with dye ink.
That dye ink is what makes it pop!
Same paper with pigment ink is blah.
which dye inks? A significant factor for gamut is the ink set, not the paper. I haven't used dye ink for quite some time, and while I know the results can be super smooth and you can get the best dMax, I wasn't aware you could get a larger gamut.
As far as maximum gamut, I don't know if there is a single paper that will deliver the best results for all inks/printers. I guess I"m confused as to the need for a "reference" paper by the OP, just not sure why that's part of the criteria.
Currently both the 49/79/9900 inks from Epson and the 64/84/9400 inks from Canon deliver some impressive gamut gains over previous generation printers on whatever paper they are used on. Hard to actually compare the two because they exceed each other in certain colors. Output from either is pretty impressive though.