I usually don't print with ICC profiles and print with no color management from PrintTool, and when I am printing from Photoshop I will just leave it as "printer handles color". Next time I print one of these large ones l will compare the difference between printing through photoshop to see if that internal conversion from graygamma 2.2 to sRGB is causing some of the additional spooling time compared to no color management from PrintTool. This is stuff to keep me occupied when these things take so long, but otherwise I'd never worry about it.
Thanks again,
Richard Boutwell