I just plotted the difference between a 3880 using Archival Matt and Premium glossy, there is a difference but again, not sure it's going to help that much and none of this has anything to do with Adobe RGB or sRGB. ColorThink Pro reports the gamut volume this way:
Matt 455,879
Glossy 768,295
But the real interesting analysis is of course looking at the two in 3D:
As one would expect, the differences are up near Lstar of the paper white and indeed, as the numbes above show, there is a larger gamut there but I don't know what will result from the actual image. I could plot that too if I had a low rez (1MB or so) and we could see if any image colors fall in between.