If you are turning the OD, you should be able to run your steady rest at a little over halfways down the tube. The part must already be perfectly round if running in the steady, as any egg shape running within the steady will be duplicated in the turned surface.
That means you should only be cutting a piece with an effective supported length a little more than 50" long. That amount should cut pretty good without deflection.
What kind of tooling are you using to cut with?
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)