I've enjoyed the "adjusted" versions of Robert Johnson's work. There's a crowd that says Johnson's music was recorded at 76 rpm, and when playback happens at 78 rpm the pitch of the voice changes (it becomes higher, ala the chipmunks). The slower speed lowers the tone of his voice, and definitely gives the blues more time to develop. It's an interesting theory, just like Johnson's life and death. If you're a Delta blues fan, give the adjusted speed playlist a listen and see what you think.