I know this depends on genetics, training, diet, etc., but what has experience shown you. Remember improvement can come through technique enhancements regardless of strength gains. I like your suggestion to change rep ranges every 3 weeks. As far as sets go I feel 2-3 are adequate. This does not include the warm-ups.
Endurance is a bad term to use.
But look back at many of my previous responses on rep choice. I believe in varying them every 3-4 weeks or so. No one rep scheme is best, in the medium or long term.