Thanks folks. The two tunes are in fact closely related already. The underlying musical structures are similar (unsurprisingly, as they support the same lyrics and story). You are right, Grishka, the ballad (which came first) fits the lyrics better in terms of imparting emotions, while the blues version (which is in a major key) lightens the song and turns it to angry/bitter rather than "woe-is-me" sad. Some people prefer the blues version for that very reason (Vanessa was the first, and she has won me round). I like both, but the blues is more fun to sing.