Well, my setting isn't realistic as I turn down the force feedback effect but it will make you go faster. You might wanna run with force feedback for awhile until the wow factor wears off then try this setting when you're ready to go faster.
Logitech setting
Overall Effects Strength = 30%
Spring Effect Strength = 0%
Damper Effect Strength = 0%
Enable Center Spring = Checked
Center Spring Strength = 5% (or 0%)
Report Combined Pedals = Unchecked
Degree of Rotation = 300' (Adjust this to suit your style. 300' will make it almost 1:1 ratio with McLaren)
Allow Game to Adjust Settings = Checked
In game Advanced setting
All 0% except
Brake deadzone = 2% (to resolve slipstream bug)
Brake saturation = 10% (if you want sensitive brakes which I do)
In game Force Feedback
Env Effect = 0
Force Feedback Strength = 100
Wheel Weight = 100
Override Input Device Type = Steering Wheel (This is important when you made changes to default G25 profile and changed to Custom)
Again, by using this setting, I shaved 1~2 seconds on every track right off the bat. If the wheel feels too light at first, try increasing the Overall Strength Effect in Logitech Setting.