Consegui acertar bastante com isso:
SELECT *,
( (1.3 * (MATCH(strTitle) AGAINST ('+john+smith' IN BOOLEAN MODE))) + (0.6 * (MATCH(txtContent) AGAINST ('+john+smith' IN BOOLEAN MODE)))) AS relevance
FROM content
WHERE (MATCH(strTitle,txtContent) AGAINST ('+john+smith' IN BOOLEAN MODE) )
ORDER BY relevance DESC
