I understand it that the doctor DID save Davros the first time and that was what basically "changed history", because he obviously saved a bad person who then later created the Daleks that were out to destroy the doctor and are basically one of his biggest threats. That's at least what I took away from it and in the end it rather looked like he wanted to "correct his mistake", although I'm quite sure he won't kill Davros either way... besides: There are fixed points in time - that's what was always said - and if he changes something THAT big, I am not sure what's going to happen... like if he kills Davros then there will never be Daleks and Gallifrey won't be destroyed and there won't be a time-war whatsoever, so whatever he does or whatever will happen: Davros is gonna live anyway...

Not so sure I liked the episode, especially know that I know Clara will be gone way too soon. Jenna already IS, and I have no idea how long she'll still be around... That kind of dampens the mood a bit for me as I love her, but well... it is what it is.