Burke, you just reminded me of something else. I asked my husband how much lower than usual a song had to be before he found it uncomfortable and how much higher it had to be before he found it uncomfortable. His answer was that two full tones lower and it became difficult but it only had to go one tone higher for it to be tricky, or uncomfortable. So I wonder if that's a function of the original key or a higher level of discomfort with something too high rather than too low.