Digital BW, The Print

If you can swing the price of the 4800 and studioprint (when 
supported) you will get the most flexibility. It seems that the 4000 
only has 7 heads addressable at any one time while the 4800 has all 
8. This opens up a lot of options when you buy a compatible RIP to 
drive it. After that you only need to decide if the 3 black inks will 
do what you want, or if you need to go with 5 black inks and CMY for 
toners, or maybe 8 blacks if that is what you need.

By turning ink channels on or off, you could have a printer that 
works with matte or gloss papers without having to change the inks. 
Advantage would be 5 blacks for matte papers, and 4 for glossy. This 
last part could be (mostly) done with the 4000, except you will only 
ever have the 4 blacks plus CMY (7 channels with switching black 
channel).

Just my 2 cents, I'm sure others will voice their opinion.