Of course I prefer the 4-5-6-1-2-3 order to be watched first,
but I think the 4-5-1-2-3-6 is really a good option too. Flashback PT appearing after the Ep5 father reveal makes sens, then continue with the conclusion in Ep6.
Plus the final space battle of ROTJ is still the best looking battle of all 6 movies IMO, so it would not be too jarring compared to the special effects of the PT.