Yes, it (black) is visible and measurable, especially on matt papers, but not only.
As for the gamut, I have made some research comparing dozens of paper vendor profiles for the old and new series of Epson printers for both 8 and 10 inksets. In most cases (>90%), in numbers, gamuts for the new ones were slightly smaller than for the old ones as on the figures in the first post. Also when I have made my own profiles for 8 ink case machines. The difference is not big, visually can be negligible, but tendency is obvious. Assuming that black is deeper, gamut volume should be wider, so a few percent shrink is evident.
Perceptually, prints are virtually the same, maybe a bit smoother in the new series, with some drawbacks in blues compared to Canons or HP, but with crazy greens and excellent warm tints.