8192 (actually something slightly smaller than that) is the maximum length for a record in SQL server and therefore is the maximum length of an individual record in SharePoint. The limit comes from the fact that SQL uses an 8K page size and records are not allowed to span pages. However, I believe that multi-line text fields are stored in TEXT fields. They are just 16 byte pointers to a different page in the database. The result is that it’s not counted in the maximum record length.
Although I’ve not tested to find a practical limit from a SharePoint perspective, I can tell you that technically SQL server supports file sizes up to (I believe) 2GB in TEXT and IMAGE fields. (It may be larger I’ve not looked in a while.)