The HP that comes closest to Epson in terms of quality is the Z3200. It's much less expensive than the Z6100, has additional gamut-expanding inks (Red, Blue), a Gloss Enhancer for dealing with gloss differential, and clogs infrequently. It's relatively slow, however, and the cost per sq-ft will be higher than the Z6100 or 11880. Both the Z6100 and Z3200 have neutral black inks, so (unlike Epson) you can print highly archival black ink only B&Ws that won't be subject to metameric shifting.
We have in-depth reviews of both the Z3200 and Epson's latest x900 series printers on our web site.
Product Reviews
You may also want to consider a RIP for productivity enhancement (nesting, tiling, rotating, etc.) and to simplify your color managed workflow.