I'd say it depends more on the paper, the profile and the custom black-and-white inkset than it does on the printer.
If you can create the media presets, the ink chemistry (or ink choices) then that is correct. Considering the matte black inks (including HP, Canon, Epson) Eboni MK from MIS inksupplies is actually the most neutral (and very stable in many ways) and MIS has also a new PKN in development that is more stable on the printer. With QTR as the driver and good partitioning + a neutral paper quality you would have a strong contender with customised Epson printers. If Paul Roark adds some nice curves/profiling to that combination it can be a winner. Though he might go for 2-3 color inks extra to make that printer a more universal B&W printer.
Custom solutions are almost all Epson based. The True B&W RIP for the Canons is using the Canon OEM inks, no other ink choices possible according Bowhaus. I have an experimental custom HP desktop printer setup but it is difficult to transfer that solution to a wide format model like the Z2100. Not impossible though. Other 6 channel (CAD) models of HP have quite large droplet sizes, the Designjet 130 might be possible with its 4 picoliter droplets. It will cope with the modern Vivera pigment inks I am sure despite being a dye ink model. I would not risk the use of piëzo head inks in thermal heads, the other way around is without problems like the use of HP Vivera pigment inks in Epson models has shown. It would be interesting to have a go with the Canon CAD 5 channel models like the iPF510 and upwards. 4 picoliter droplet. True B&W RIP does not support them though (I have asked why not? but got no answer) There are some quirks in the Canon CAD driver though that would make it hard to use that driver with custom B&W curves in Paul Roark style.
Out of the box and with a slightly less neutral matte black ink (compared to Eboni) and with the other gloss monochrome inks being the most neutral of all right now, the HP Vivera pigment printers are in my opinion the best choices in that case. Add to that the excellent fade resistance of the HP Vivera pigment inks and the media presets not having composite (CMYetc) grey mixes, the Z3100 + Z3200 are hard to beat on B&W neutrality with proper neutral paper choices. With 6 extra hue inks to steer B&W prints from neutral where desired or to build an adapted B&W tone range on non-neutral media. Not to mention splits. The Vivera pigment color inks are second to none in fade resistance. Fade resistance is important with B&W, any hue shift along the tone range is more visible in a monochrome image than in a color image. There is also the severe ruler of silver halide B&W print longevity we measure B&W inkjet longevity against. The choice of gloss/satin media for the HP Vivera pigment inks can be tricky. Even with the full dose of gloss enhancer ink there are several gloss papers that show bronzing which is a real issue with B&W prints. The post iPFx100 Canon pigment models do better on that aspect.
Met vriendelijke groet, Ernsthttp://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.