I've completely stopped worrying about range alltogether. Instead, I've been focusing on intonation and sound. That seems far more important to me at this stage... Used to be I could reach some D's and maybe a few F's for an hour or so then I'd gas out. But this weekend I was playing double-G's well into a three hour gig. Why the drastic improvement? I don't know and I don't care. I think if you obsess about the range, you'll always have your focus on the wrong things. Worry about music, intonation, SOUND, and the range will take care of itself.