Wow, more SW/Who connections!
I can't recall when the Master got more hostile towards the Doctor. I guess reaching the end of your regenerations, then stealing yourself a new body to cheat death makes one more evil and twisted?
In the Pertwee era, I got the impression the Master was like Moriarty to the Doctor's Holmes. There was some mutual respect, but no real malice. In other words, he wasn't going to kill the Doctor unless it served his purposes.