This is interesting, thanks for sharing Dave.
We recently did a quick test with a R2880 to determine the number of prints per set of carts. We started with a full set of Piezography carts (about 15ml of ink in each cart), and printed an 8x10 gradient on 8.5x11 paper, using the 3880-MPS-Type5 curve at 2880dpi and uni-directional speed (best quality print settings). I see Red River printed @ 1440dpi thru the Epson driver, so the resolution and printer driver differ in our tests, and effect the results. For the seven Piezography shades used in printing= 105ml of ink total, we got 50 prints before the printer indicated a cart was empty (though some still had quite a bit of ink remaining). Figuring $.46 per ml (based on a 110ml bottle), this equals less than $1 per print. We were able to coat 16 of these sheets with GO from the 15ml cart (equals about $.43 per sheet to print GO).
Matte/rag printing will be slightly fewer prints per set of carts, since the matte/rag curves have higher ink limits than gloss curves, but don't require the GO coating.
This can be transferred to other K3 printer models, which use the same curves.
I hope this is helpful, best regards and happy printing~ Dana