I am primarily a DS3 player, and as soon as I heard about the steering sensitivity option I turned it up to 7 and I haven't looked back. It makes a huge difference when driving the F1 cars. I went from winning Indy at the seasonals by 7-8 seconds to winning by 15 seconds. I also went from not being able to win the FGT championship to sweeping it with golds. I've not yet tried the Vettel challenge since the change, but now I'm really anticipating it. In my opinion, this was the most significant change with the new update.
I also have an $80 wheel from Gamestop that I haven't really grooved with. I'm hoping the sensitivity setting helps with it as well.