Technically, adding a hard disk to a LaserWriter IINTX does slow down printing. This is because when searching the font list (ROM and disk-based), the system searches the entire list (even though the font may be in ROM) and sends one packet for each and every font. Further, the search continues through the list even after the desired font is found. Engineering is aware of this and is planning to fix it in a future revision.
When printing using a font not contained in the LaserWriter II ROM, the fastest printing is achieved once the font is held in the LaserWriter II RAM. Fonts downloaded from the System Folder result in the slowest printing. Printing with fonts stored on the hard disk falls somewhere in between.
Depending on the context of your discussions with Adobe Technical Support, their statements could be accurate. Most of the information we gathered in previous discussion.