James,
Mike and I have had some conversations outside the forum and I just noticed there is one bit of info left out that might impact the choice of materials. "extra long" means > 18" in this case, maybe even 24". With a tool post arrangement, there is an awful lot of leverage out at the ends. I would not be concerned about breakage (it is a concern, but these are spindles of around 1") as much as twist to get slightly out of alignment. If you are trying to make consistent diameter tubes, staying aligned is important as you can slide a tool along without letting it slip through your fingers or use a mark on a tenon cutter.