[voltagex_]

The only thing is that the 4M and 5M probably use a large amount of power compared to their modern counterparts - anyone got any measurements?

You should be able to throw most dialects of PCL and PostScript at those printers and they'll work fine, so this fits the GP's requirements (not having 500mb of software)

Anyone know how to make Windows speak PostScript?

[Gracana]

Yep, printer drivers are already available in Windows, which is nice. According to the manual, the 4m uses 195W when printing, and 55W in standby. The 5m is 300/80, and 22W in "power save" mode. I'm guessing that's a mode where the fuser is fully cooled off, so it's probably slow to spool up if you enable that.