When a user overflows a TEXT cell size with a single post that's 64 Kilobytes of text in in the single database cell; a MEDIUMTEXT (the default size of a PHP text string) is the next size up as far as database text types go, and is really untested with the UBB.threads system (I'd make a copy of your database and convert the cell and check if everything is running without an issue before you proceed). The MEDIUMTEXT allows 16 Megabytes of text into a single cell, and users really should not be inserting that much text into a single posting..
