First off, you "don't" need to do a print every few days on the x400 or Pro series since their heads are built better than Epson in that area (more nozzles and many sensors to keep the head functioning properly).
I really don't know where you guys get your info. To be honest, every one of your responses always sounds like you work for a marketing company rather than an end user. Sure you might have many printers set up in your offices and use them all the time, but since none of the employees actually owns these printers, you don't care about the running costs, and since many people perhaps use these printers, you really don't have a good measure on what is needed as minimum printing. Maybe you even use it often enough as to negate any reason for keeping track of this.
PS. I'm a happy Atlex customer and have bought 2 printers from you and lots of media, but I just don't like the advice you give on this forum.
Moving along, and in response to the original poster, here are my direct findings with a Canon iPF6400. I have also owned an iPF6100, so I'm quite experienced with these printers. As has been said many times, the secret to these printers is they have to be used. How often? I would say every 2 days.
I have gone away twice. First time for 7 days, and I turned the printer off. When I turned it back on, of course it needed to do a clean cycle, and went through about 50ml of ink. Surprisingly, this doesn't really match the amount of ink used for different clean cycles. There is a low clean cycle A, which is what I believe they call it, and this uses about 14ml of ink. The more aggressive one should use about 90ml from my understanding. So how mine used 50ml of so, I'm not sure, but perhaps it did something a couple of times. Its a fair amount of ink to waste just to go away for a week in my opinion.
2nd time away was for almost 2 weeks, and this time I decided to leave the printer on. I thought maybe by being able to do its own routine, it would use up less ink. Well, after my return, I tried to do one print, and it first did a clean cycle, and by the time it was ready to print, over 80ml of ink was used up since before I left. Now what I didn't do was see how much ink was used up before I tried to do my print, and this is a shame, but the end result was that I learned to never go away! LOL
If I wait more than about 3 days to do a print, it will use that standard 14ml of ink to run a simply clean cycle. It might not seem like much, but with the small carts, and adding on taxes, you're looking at about $1 per ml. This 14ml of ink can actually print quite a few pictures, so its such a waste. Now if all I do is print a simple pattern I got off the internet on a letter sized piece of paper, I use 0.4ml of ink, and it never does a cleaning cycle. I have not had to do a print for over 2 weeks, but as long as I keep making sure to do this print pattern every 2 days, the printer works just fine without doing a clean cycle. I alternate between telling the printer that the paper is just plain paper, since it will use matte black, and then I say its glossy paper, so it uses photo black, but I still print this out on regular copy paper. The glossy setting uses about 0.6ml of ink vs. 0.4ml. As you can see, doing 3 or these prints a week, I'm looking at less than 2ml of ink per week for maintenance vs. the dreaded costly clean cycle of leaving the printer off. I would like to see if I can stretch this out to doing a print every 3 days, but frankly, I don't even want to waste one 14ml clean cycle. It sucks that business is so slow that in the winter I may not have to do a print for weeks, but this is how it goes.
It amazes me that the printer isn't programmed better. If I go to the trouble to do a 0.4ml print every 2 days, it will run perfectly for weeks without a clean cycle, but the minute I don't print anything for over 3 days to a week, so much ink has to be wasted. If I ever go away again, I'm going to look into using one of those script programs to automatically send a print to the printer every 2 days and just load up a roll so it can print on that, cut the paper, go to sleep, and be ready to print again in 2 days.
Now I do think that even 2ml of ink per week isn't really enough for the printer cause this is spread out over 12 channels. Ideally, I would have actual prints to do every week so that at least 10ml of ink was used, and sometimes I do print out some pictures that are my most popular since I know these will eventually be ordered, but at the very least, the printer counter does think its being used regularly so it doesn't automatically do a clean cycle.
These are the things a regular guy has to keep track of. In relation to my message above to Atlex, they of course don't care if they shut the printer down for a long weekend lets say and have to go through a 50ml clean cycle when they turn it on because they aren't really paying for the ink carts they need to replace. But for an end user, this would be deadly. Imagine having to do this just twice a month, and hence wasting $100 of ink. This is a real cost that no individual owner should have to put up with. Luckily there is a workaround, and it only takes 3 minutes to do a print, but this is in fact what you have to do if you want to be very efficient with your printing costs.