Digital BW, The Print

Has anyone compared the ink waste on printers using a Cartridge 
system vis a Continuous Ink System (CIS)?

Or, do I have a printer from Hell, as Jon Cone referrers to some 
printers?

The reason I am asking is that I have two (2) Epson R2400 printers.  
One printer uses a cartridge system which I fill with K7 inks and the 
other printer use a CIS with K3 inks.  The CIS is pumping (wasting) 6 
times the ink then the cartridge system.  (CIS = 120 ml vs Cartridge 
= 20 ml for about the same amount of printing)  

The reason I know the amount is that I have added overboard waste 
systems to both printers per the following website. 
http://www.inkrepublic.com/KnowledgeBase/R2400WasteInk.asp

I am aware the Epson R2400 waste more ink then some other printers 
but I can not change that.

Any information will be welcomed.

Bill LaFever