2566B = 900 LPM.  A good solid printer but not the fastest in the 256x
family.  Please add dropping of this product line to the official list of
"dumb" HP decisions.  Not everybody can convert everything to laser based
printing.

Basic math:

900LPM / 60 = 150 lines per second

150 LPS * 132 char per line = 19800 bytes per second

I believe that "bps" is "bytes" or "baud" not "bits" so 19.2K transmission
speed is comparable to the printer's maximum speed.

I would suspect that the 256x printers will strip trailing spaces (null
stripping is configurable) but the printer cannot know that there are no more
non-space characters in a line until it has received the entire line.  Yes,
the spooler could be stripping trailing spaces though.  Note that these
printers print a line at a time so the speed advantage with 'short' print
lines really isn't there for the mechanical speed.

Carriage control can make a BIG difference.  10 lines of 132 blanks vs. a
single control code to skip 10 lines for example.  That could be a way to
regain the 'lost' speed.

Please keep this discussion going with whatever you find.  I have a client
with two 2567Bs to convert over to serial shortly and I'm curious why you
have this happening.

Wayne Boyer