We have a HP Laserjet 9050dn server and are not getting the reported 40ppm throughput.
Throughput depends on many things, most of it is rated at the very basic printer settings. Typically it is rated for paper type settings set to plain, anything else may slow the printer down to accommodate the media type, as well as letter or A4 size paper being selected. Also, the data connection type and speed (network/server loads, print server loads, etc.), as well as the complexity and size of the data being sent, and the speed of the computers generating the data fast enough to maintain the printer with data to keep it printing without having to wait, all play into how fast the printer will print. There is no easy answer as to why you're not getting the speed you expect. It would require detailed analysis of your setup. Also, make sure you're using a PCL driver instead of PS (PostScript) as that will also make a difference.