I just recently got a logitech driving force gt. I would like to know the most realistic settings out there. Where it actually feels like a real car. Thanks.

The common wisdom is to have 100% for Overall effects strength. 0% for Spring effect strength, and also 0% for Damper effect strength. Tick the "Enable Centering Spring" option, but set at 0%. Degrees of rotation is personal preference, i normally run somewhere between 270 and 360. Tick the option to "Allow Game To Adjust Settings".

This tends to be the base to work from. You then tweak the in game parameters to get a feel you like. Be aware that some Logitech wheels have reverse effects so if the forces feel backwards in game set your FF to a minus value or look for a box that says 'reverse effects' (both in the game itself).

Like this I'm guessing?

Yes. You might find 900 degrees a bit much. Just depends on personal preference and what sims/cars you are using.

That's how mine is set too, sometimes at 110% on effects and I keep to 350° degrees. That 10° seems to make it feel right somehow.
A couple of games are better with the "allow game to make changes" unchecked. IIRC Shift 2 is like that and some other one. Usually I have it checked.

Degrees settings is all about the mod or sim. What I do is practicing with the car to adjust the steer ratio between the in-game steering angle and the wheel, and then I put the in-game setting at its max and adjust the wheel setting to keep that ratio.

I personally have tried many different things with it, but I find the best performance is at default with the Allow game to adjust settings selected... And then editing in game...