It's a shame though to run the 9900 for printing 5x7s and 8x10s.
On the other hand... its good that its not just sitting there as a printer being used every day is the best preventative maintenance! So maybe those 5x7s will do it some good. And you're getting better ink costs I think with the larger carts as opposed to using the ink in the smaller printer!
(of course you're losing this in the extra work it takes to do small prints on a big machine.
)