I am having this exact same problem on Mac OS X 10.8 with the latest printer drivers from HP, 19.9. Medium and large size print jobs take forever to spool. I have waited upwards of 5 minutes just for a PowerPoint presentation to print out. The firmware is fully updated, as are all programs and the OS on the computer.
I tried connecting a different HP 2600 to the same network port, and changed the drivers to the most recent for that model, 1.4.0, and had no issues printing at all. This is definitely a driver issue.