Pat,
I have no experience with the P600, but in general the "Eboni" based carbon inksets I use and describe in the various PDFs I've published have been more lightfast than the OEM "Advanced B&W" approach, and they can also be vastly less expensive.
When the "generic" base c6b is used to dilute the Eboni MK, the resulting inksets have been the least likely to clog of any, including the OEM inksets, that I've used. The reason is rather simple. The c6b base is for matte paper only and has no binders (glue) in it. Binders are needed to stick pigments to glossy papers, but matte papers don't need any binders at all. The binders are a major factor in clogging.
In real world work with wide format printers, I find the Eboni MK clogs from simply drying out if not used about like the OEM MKs I have experience with. The dilute carbons, on the other hand, are way less likely to clog. When there is a gap in a nozzle check with the dilution inks, it's usually just a bubble of air that has "invaded" the head due to it having sat too long and not been used.
If you are comfortable with old wet darkroom chemicals, you'd be able to make the dilution base yourself from the formulas I've published. MIS Associates (
www.inksupply.com), which commercialized my open source formulas, has also listed the formulas for it's pre-mixed generic base. (I always use version c6b.) If you make your own base, all you need is the Eboni MK. The only problems I've heard of from the use of the base appear to relate to the use of water that was not distilled -- that is, bad water.
There aren't many areas where the least expensive option is also the best, but if you are a B&W photographer and print on only matte papers, the "Eboni-6" based carbon inks, with DIY mixing may be such a case.
Paul
www.PaulRoark.com