In Logitech Software settings everything is at 100%, centering spring is disabled, wheel rotation is set to maximum 900°, and the box "Allow Game To Adjust Settings" is ticked.
(Maximum wheel rotation of 900° is used with Soft Lock in game enabled, so the game choose the real wheel rotation according to a car.)

The best FFB feeling and handling seems to be if Self Aligning Torque, Suspension and Tyre Friction are similar values. All of those can be then moved up and down accordingly for stronger or weaker FFB experience. (Optimal value for me is between 50 and 75.)

Self Aligning Torque is the main force of FFB, containing most of the important information about forces created by the tires and suspension geometry.

Wheel Friction is mainly just plain friction and damping of the wheel itself, which makes the wheel only harder to turn and degrades all other information and details on those G25/G27/G29 wheels. So I recommend setting it to 0.

Tyre Friction is probably the friction of the tires to the ground only when car is stationary. But it seems to somehow positively affect FFB feeling as a whole if set correctly.

Suspension reflects roughness and bumps of the road etc. If set too high on those G25/G27/G29 wheels, it just rattle a lot and ruins the experience.

Collision has effect only in collisions etc. I recommend to set it accordingly to Suspension setting.

Soft Lock limits wheel rotation according to the real wheel rotation of a car, if Soft Lock is enabled. It is just a hard stop, so I recommend setting it to maximum if used.

Steering Centre Force just centers steering wheel at the start of a stage, if the wheel is off centre.

Everything is default here. (Or according to personal preferences.)

I just recommend to set small Clutch Deadzone and lower Clutch Saturation a bit for better clutch operation when using a clutch pedal.