I bought the 7890 about 6 weeks ago when Vistek advertized the "Golden Ticket" (additional $500 off the printer).
I was using the 3800 with extremely happy results on Ultrasmooth Fine Art and Ilford Gold Fibre Silk. Perfect renditions on paper, matching the screen (calibrated).
I set up the 7890 then discovered that not so many of the paper makers (Illford, for example) had updated their profiles. Oh well, stick to Epson for now, fair enough. Instead of photo paper I decided to try the Epson Hot Pressed Natural and picked up a 24 inch roll. The near blacks were totally muddy. I did a side by side print from the 3800 and there was nothing to compare, the 3800 was exactly matching the screen, the 7890 was muddy. After tweaking the file in CS5 I could reproduce "somewhat" close to the 3800 print.
In the end, I went to California on a business trip and came back with a Spyder3 Print system, created a profile for the Epson paper, ran the printer via Photoshop Manages Colour and Voila!....perfect prints again.
How is it that Epson's profiles could be that bad?
On the ink usage values, I'm running between 1.5 and 2 ml per square foot, noting that I tend to have dark subjects/backgrounds so may actually be slightly higher than typical. No complaints on cost of operation, just the poor profiles.