I just think the AI plays smarter with it at 50. They do take more shots down field and throw the 15 to 20 yard routes as well. I think with it lower they dink and dunk and have high completion % but go a bit braindead and go with 5 yard routes on 3rd and 10.
I'm seeing 55 to 70% completion from the AI but they seem to play intelligently and they don't really feel like Robo QB.