Hi David,
The 32Mb limit only applied to the text content of the document, not to the overall file size. The file size limit for Word 2007 & later is 512Mb.
As for master/sub-documents, these have been very unreliable over the years. See:
http://word.mvps.org/FAQs/General/Wh...ocsCorrupt.htm and
http://www.word.mvps.org/FAQs/AppErrors/CorruptDoc.htm
There really isn't much that Word's master/sub-document offers that can't be achieved via separate documents linked with INCLUDETEXT and RD fields.