I use a DFGT with FF set to 10. I found lighter settings less realistic overall. Somehow the steering doesn't feel quite right, too stiff at times and too light at others when compared to real life. 10 seems the best compromise to me.
Steering on real cars varies immensely, from cars with no power assisted steering, to cars with huge steering wheels from the 70s, to variable weight steering to modern cars which allow you to adjust steering weight so I suppose that would be quite hard to mimic in the game.