The "page-per-minute" specification in all of Apple's printers reflects the maximum number of pages per minute that the print engine is capable of outputting. The key factor is the speed that the print engine can output pages. This defines the theoretical pages per minute if the I/O board can process the pages as fast as the engine can output them.
We would be very surprised if you are able to get 8 pages-per-minute from a Personal LaserWriter NTR. We printed all blank pages (to take out the variable of rasterizing the page) and verified that the printer could only print approximately 4 pages in one minute, or roughly one page for every 15 seconds.
The same page-per-minute specification denoting print engine speed is used industry-wide.