How to compress 14 GB of csv files with 7zip (minimizing space)

If you want compatibility with the Zip Folders capability built into Windows XP, you're stuck with Deflate compression. I don't think you can even use Deflate64, much less the advanced compression methods (like LZMA, PPMD, WavPack, Bzip2, etc.) available in recent versions of winZip and PowerArchiver. PowerArchiver at least defaults to using the .zipx extension for those files -- I don't think WinZip is doing that yet.

The smallest possible zip file that 7-Zip can create can be done with the following command line:

7za a -mm=Deflate -mfb=258 -mpass=15 -r C:\Path\To\Archive.zip C:\Path\To\Files\*

Of particular note: 7-Zip's wildcard parser is not the same as most others on the system. *.* means all files that have extensions. * means all files.

Creating .zip files this way (and, presumably, using other tools that attempt to make smaller "standard" .zip files) is really, really slow. You would most likely save considerable time and space by using 7-Zip or WinRar to create self extracting archives.

The content of the PDFs (text & images) is probably already compressed -- so there's not going to be much to gain by trying to compress them again.