Mark,
I will not be using the Epson PK, LK, & LLK. The core is going to be 100% carbon, and Epson's (and all OEM) grays are not 100% carbon to be best of my knowledge. They are blends of carbon with color pigments to make them more neutral, which is what their function is in color printing.
I will probably use the MIS PK as a starting point because it is pure carbon. The MIS carbons from their K4 and UT7 inksets is what I've used in that past with good success. This gives a warm end to the printing range that is half way to sepia but has no yellow in it the way the OEM inksets must get to that tone.
The only B&W pigment print that I have in my house that shows fade is a sepia tone print where yellow and magenta needed to be added to the neutral gray inks to make them that warm. Thus the old photo reproduction project I did for the local museum was printed with the MIS glossy carbons, and those prints have held up very well, even in "outside" (but under glass) display for 2 years.
While MIS glossy carbon can reach a lab b of more than 13 on glossy paper (see
http://www.paulroark.com/BW-Info/4000-6K-Plus.pdf at page 7), the interesting thing I found in working with the Epson 4000 with MIS glossy carbon is that it is only slightly warmer than Eboni on Arches watercolor paper, which, as you know, is one of my targets for printing because it is not a coated paper.
I have a very healthy respect for the OEM ink technology. They have some excellent color pigments, not to mention the also excellent Claria color dye technology. However, the OEMs, like the vast majority of digital cameras, really must serve the color market first. They like to show off good B&W prints in their ads, and they aren't bad, but by making an inkset where almost all the positions are carbon, we can end up with a system that, for B&W, has some advantages.
Relative to the 4000 K6-plus inkset noted above, one of the compromises I'm going to make is to use a pre-mixed color toner to offset the carbon warmth. I think the ease of profiling offsets the flexibility of having both an LC and LM in the printer. A single toner also allows very easy Epson driver control via Photoshop curves, which can be embedded in ICCs.
I'll use my 1400 as the first platform, but I'm obviously looking to scale up to wider formats after that.
Paul