I think you will find that the 9900 has a huge difference in many areas over the 9600. It will be definitely faster at least 2x maybe 3x. This is due to many new design features, like the greater number of nozzles. You should be able to get a very fast print job at 1440 and not bad speeds at 2880. There are others areas too, like paper loading which on the 9900 is much improved (at least for roll). Noise, much more quiet printer.
Congratulations on the upgrade and enjoy.
Paul Caldwell