At delta they only fly the 764 as a single type. They don't mix in the 757 or 763 so they are much more proficient. To be honest I don't know what the tail strike angle is on the 763 compared to the 764 as I have only flown the 762 and the 764. I can tell you that performance wise and pilot friendliness especially on landings that the 764 is nothing like the 762.
As far as the 739 is concerned I had said that boeing should have stopped at the 738. New design was needed instead they wanted a cheap alternative, hence the 739. Went to the boeing factory this summer and they were touting the 739 as a replacement for the 752. I interjected and said that maybe it holds as many passengers but performance and capability between the two are light years apart! So then I asked when boeing would come up with a comparable replacement for the 757. Crickets......