I have used the GS supplied HP750 driver since I got the Oce in 2002...(I think the 750.. I'm not on that computer, but I don't remember noticing any difference in them anyway). It has worked fine for every version of the OS and AC. The only problem I have had is now via Airport. So, since you are not wireless I am no help. I think I did play around with the Oce driver, but for some reason I went back to the HP driver, but I just don't remember what the difference was. My understanding is that the basic HP driver is somewhat generic so less likely to cause issues trying to do too much. I have had no reason to try anything else. The Oce driver might offer a few options (like collating and scheduling) but not on the Mac, but only if you are plotting to Oces printing program, which is Windows only.
So, just my best guess is to try the GS HP driver and see if it simplifies the output and avoids something that is causing the error. I don't understand a postscript error plotting anyway. Postscript is a print function, and you said you are plotting. I am plotting, not printing, a big difference. My Oce does not have a postscript card, so i have to plot. I prefer plotting anyway as it is faster. I once tried a postscript card in the Oce, but had problems so took it out. Are you plotting or printing? You shouldn't be triggering a postscript function plotting, as far as I understand it... but I avoid knowing too much about that stuff:)