I always assumed that using the 'Presentation' option in the print dialog would produce a better but larger file plotted to pdf...
Just comparing an A1 drawing plotted out of RAC 2011 to pdf - 'High' option gives 2.2 MB whereas 'Presentation' gives 1.3MB file size.
Strange - comparing the pdfs the 'High' output version does seem sharper than the 'Presentation' output - perhaps more anti-aliasing in the Presentation version?