6MB is actually very small when it comes to PDF files. Are you printing right from within Outlook, or are you saving the files first to a local directory and then print from there? If you are printing from Outlook, try saving the file first. It is possible that the performance problems are caused by the printer driver. In my experience, most printing problems with Acrobat and Reader are fixed by the newest available driver (which should to be newer than the release date of Acobat), so upgrade your printer driver and see if that fixes your problem.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com