I run genuine HP inks as the after market that I have tried is not much cheaper than my supplier, and usually run out faster and do not look as good. I run probably 3 and sometimes 4 (yellow) cartridges of ink before changes and before banding appears. The banding is most apparent in dark colors, especially reds. Our prints aren't going to be the 100% best available, but I'm not selling prints either (find my introduction thread to get a better idea of why).
I have 3 5500's that I run all day. Ours run 8-20hrs a day and rarely break. I have had HP out here several times over the 3 years I've had the machines, for various reasons. Typically I'm printing cheaper water resistant poly, and an adhesive backed Kodak poly for mounting on coro, etc. Usually 6-8 rolls of a WR Poly a week on one printer, 4-6 rolls of the adhesive on the other, and on the 60" I'll run 3-4 rolls of different medias a week. Thats a conservative estimate I'd say.
The prices are dropping quick on them, and I'd bet you'll see more for sale in the 4000 and cheaper range soon (42" versions).
I'd also suggest you deal with, or at least attempt to with Unica Digital. I just recently purchased some parts from them and couldn't be happier. Great guys up there to deal with and very knowledgeable about the HPs and other digital printing options.
