Are you saving in 2004 format? I know 2004 has a compression built in.
I don't quit understand your question, e-mail me the drawings and I'll have a look.
BTW... We deal with drawings ranging up to 15mb and some with images that have plt near 30mb and have no trouble plotting (yes the plotter receives them very slowly, but they plot). We're using an HP 1050C with 512mb memory. What do you have that won't plot a 5mb file?