I find that the difference between 1440 vs. 2880 is very subtle on my 4800. The biggest difference that I notice is that the 2880 looks like it has more ink and that the colors are a more saturated. This might be a good thing on some pictures but I generally prefer the look of 1440.
I notice that in a picture with a blue sky with some very white clouds, the transitions from white to blue does not look as natural when printed in 2880. I have never tried to find out if the printer actually uses more ink, but it does look that way, and I guess that is what matters most.