Very, very slow sending to printer

I am building PostScript print jobs that when printed to a Konica
Minolta 1050 will produce folded, stapled and trimmed 8.5 x 11 inch
booklets. The imposition is done in an application that builds it from
multiple “print to file” jobs done by other people. Since I have no
control over the input, and the multiple jobs are through different
drivers / operating systems the application spends considerable effort
converting them into clean PostScript, then imposing the PS and wrapping
it in the commands to finish it properly, and the final imposed job is
quite large.
Sending the job to the printer produced the correct output, but took
forever. I observed from the system monitor that I was averaging about
60 kilobits per second to the printer. However, when sending the same
job to a printer queue (or a shared folder) on a Windows computer I got
around 10 megabytes per second. If I sent from the Windows computer to
the printer I got about the same 10 megabytes per second. Currently the
fastest method by far is to print using the Windows machine as a print
server.
I did test for bad connectivity at the printer end by moving the patch
cable going to the printer to a laptop running an LPR queue: I got 10
megabytes/sec from both the Windows and the Linux boxes. The problem is
Linux/CUPs talking to the printer. Linux to Windows or Windows to
printer is fine.

Though I am a Linux newbie, this does not seem right. Where should I be
looking for my problem? The printer manufacturer is no help, at least,
not in the short term.

Running Fedora Core 5, on a Sun Fire X2100 (2GHz Opteron) with gigabit
Ethernet. (The printer has only 10/100.)
The Windows tested was XP Pro on an identical X2100 (and also the
laptop, a Pentium 4).