General observations to date:
The Pro 1000 delivers a significantly larger gamut over both the 9500 II and 9800. Especially lower black points and better rendition of darker colors.
The Pro 1000 driver has a better, and less lumpy, mapping of device RGB values than either the 9800 or 9500. Fewer patches are needed to create good profiles. The standard iSis 957 patch, letter size target creates better profiles. Good profiles for the 9800 requires significantly more patches.
However, the 9800, to my surprise, produces slightly more consistent colors. Printing random, in gamut, colors in different locations, the 9800 still produces the smallest differences. A large patch set overcomes the lumpiness of the 9800 driver so, when combined with a patch set optimized for the 9800, the 9800 delivers more precise, in-gamut, colors. However, this effect is not visible (to me anyway) though it is measureable. Says a lot for Epson's design of the rather old 9800.
The Pro 1000 prints appear to have less gloss differential and bronzing though, at this point, I don't have any good way to quantize the differences. This is an important, but highly subjective, effect.
Things I have not yet investigated:
How well the Pro 1000 prints fine textures. Does it do a better job interpolating rapid changes in pixel values? How much does the printer change over time and how much change occurs when not printing for a week or so.