If it's anything like my Delta gap-bed with the reeves drive, you should be able to go plenty slow with it. (my low end is about 300 RPM)
In actuality, I've found that I prefer to rough pieces as fast as I can, just short of a speed that will cause the lathe to walk around on me. There *is* a reason for that- the faster the high spots are going, the less likely your tool is to ride in to the low spots and catch. I'm aware of the contrary arguments, of course- that's just what works for me.
Especially when you're working with a hollow spindle between tapers, I wouldn't get too concerned about it. You only have a max 14" swing, and it's supported on both sides.
My opinion, of course- do what feels safe to you.