"usage note: the word dour, which is etymologically related to duress and endure, traditionally rhymes with tour. the variant pronunciation that rhymes with sour is, however, widely used and must be considered acceptable. in a recent survey, 65 percent of the usage panel preferred the traditional pronunciation, and 33 percent preferred the variant."
to me, dour (sullen, gloomy) rhymes conceptually with sour and glower, which is why i prefer that pronunciation. and in as much as the etymology of dour (severe, stern) is durus (duress and endure), that sense should be spelt dure. imo.