The only difference between the iP4000 and the iP5000 is the minimum size of the droplets. They both use the same five non-chipped BCI-3e and BCI-6 type cartridges. The iP4000 is like all the other Canon printers that use those cartridges with a minimum droplet size of 2 picoliters while the iP5000 is like the newer generation of printers that have chipped cartridges with a minimum droplet size of 1 picoliter.
Some people on this forum have complained about the iP5000 having a greater tendency to get its nozzles clogged with some third-party inks.
I'm very satisfied with the quality of photos on my iP4000 and since I have several printers that all use the same print head, I would not buy an iP5000. If I had no printers and I was offered the iP4000 or the iP5000 at the same price, I would go for the iP4000, otherwise, I would go for whichever was significantly cheaper.
Good !, because they are the better models in my opinion. I am in complete agreement with all of Ghwellsjr comments above.
The 4000 has been the best printer I have had, I got the 5200 , but I prefer the 4000 . The reason for my doubt about whether discontinued or new , the discontinued models are difficult to come by now,they command twice the price , ( second hand) , of their replacements, which should indicate the esteem in which they are held.
I also agree with ghwellsjr , the 4000 , rather than the 5000. From a refill / compatable perspective , they cant be beat.