@Martin FYI, my new answer here contains a query with (what I think) is the maximum possible information we'd get from SEDE. It gave a pretty accurate number (+7008) for my own account on Meta.
When searching for posts where some string is contained in the body or in the title I can use (Body LIKE '%##text##%') OR (Title LIKE '%##text##%') or (CONCAT(Title,' ',Body) '%##text##%').
Could the difference in speed between them be large enough that I should prefer one of them over the other when writing SEDE queries?