Comment 1 for bug 977912

It looks like the poppler pstops tool defaults to 300 dpi, compared to Ghostscript's ps2write's 720dpi. Normally, this would not matter (both will always try to preserve scalability whenever possible), but when flattening transparency, the resulting image is created at the requested resolution. Both flatten PDF transparency groups to images in a similar fashion.

I suspect a number of the performance issues with Postscript printers stem from this, so the simple "fix" is to add "-r300" to the GS command line to get comparable output to the pstops.

As stated above, a nice enhancement would be to choose a resolution which is an integer diviser of the actual printer resolution: so for 600, 1200 and 2400 dpi, 300 is a good setting. For 720, 1440, 2880 dpi, 360 would be a good setting.

FWIW, it might be informative to assess the actual operating resolution of the poppler based "toraster" utility in the cups workflow, and see if that was also using a fixed (default?) resolution.