jackfrost

Coming at it from a producer's perspective, I do think there is something to using different keys. It has to do with how the frequencies interact as you get closer to the bass region of the frequency spectrum. This region starts to get much more sensitive to playing notes that are closer together because they are slower, so you hear the beating of the clashing frequencies more. Transposing a piece up will alleviate some of this "beating". So finding the right balance for your progression with the mood you're aiming for and with the right bass representation absolutely comes into play for me.