Batch or Continuous?
Thanks for asking our advice.
I believe you have correctly identified the issues: The Lee will be faster, but the speed difference is due largely to the fact that you don't have to remove the shell from the press. You would slow the Lee down if you powder charge or prime off-press or remove the auto-indexing rod and use it in batch mode. You would speed the Redding up if you used it in a continuous mode like the Lee, but it does not auto-rotate the head like the Lee does, so is not likely to ever quite match the speed of the Lee.
If you are going to load by the batch process (Deprime 50 cases rotate the turret head to the next die, Case mouth bell, then rotate the turret head to the next die etc, etc) and you will NOT be using Lee's case mouth expander which allows charging the case with powder right through the case mouth belling die, then the Redding might be better for you. Because it allows more dies / dies stations to be available and allows more room between dies.
Drawback, you will be handling the cases multiple times, which will slow you down.
If you will load in a continuous manner (size/deprime, rate the head, case mouth bell/charge with powder/reprime, rotate turret head, place bullet/seat bullet etc and produce a finished round without ever removing the case from the shell holder from start to finish, you will probably be better off with the Lee Classic Turret.
Press flex is not supposed to be a problem with either press. The Redding, with the dies further from the axis of rotation has more off-center load to contend with, but that load is balanced by the rear support being 180 degrees from the ram exerting the force. On the Lee, the force is much less off-center and is actually supported quite well by the turret ring, very close to the line of the ram's force. Keep the support posts tight and you will not have a problem (and I have never heard of them loosening by themselves).
If you will use the Lee "Powder through" case mouth belling die (sold separately if you want to use other manufacturers' sizing and seating dies) and use the Lee Auto-Disk powder measure (or drop powder manually through the Lee die with a funnel), get the Lee Classic Turret.
If you will use more than 4 dies or a press-mounted powder measure not from Lee or will be pulling the cases out of the press for any off-press processing (for example, priming with a hand tool, or full-out batch processing), get the Redding.