I tend to lower the steering ratio because I like to have a more responsive GT3 when I turn my wheel while putting very little angle.
Don't hesitate to raise the steering ratio by 1-2 clicks if you are used to playing with more steering ratio.

TC: - I recommend the TC6.
      - TC5 for the T5
      - TC4 for the exit of the last corner

HotLap/Qualifying lap adjustement:
- Target psi tyres 27,1-27,2
- Rear Toe: decrease 1-2 clicks if you want more turning OR don't touch
- Rear Antiroll Bar: increase 1 click if you want more turning OR decrease 1 click if you want more stable
- Rear Ride Height: increase 1-2 clicks if you want more turning OR decrease 1 click if you want more stable but understeer appears OR don't touch
- Rear Wing: increase 1 click if you want more stable but lose so much time in S1 and S2 OR decrease 1 click if you want more turning and more speed for the S2 but the time gain is not huge and can make the Mustang tricky for the S1 and S3. To your feeling.

Race adjustement (advice):
- Target psi tyres between 27,2-27,4
- Rear Toe: increase 2 clicks if you want more stable OR don't touch 
- Front Antiroll Bar: increase 1 click if you want more stable but more understeer can appears
- Rear Antiroll Bar: decrease 1 click if you want more stable
- Rear Ride Height: increase 1 clicks if you want more turning OR decrease 1-2 clicks if you want more stable but understeer appears OR don't touch
- Rear Wing: increase 1 click if you want more stable but lose so much time in S1 and S2 OR decrease 1 click if you want more turning and more speed for the S2 but the time gain is not huge and can make the Mustang tricky for the S1 and S3. To your feeling.
- Front Brake Ducts: it depends on the temperature
- Rear Brake Ducts: it depends on the temperature

My best lap with this setup: 1:51.985 (on a mega lap, there is the possibility of doing .8 low, so you can improve so much my time)

Good Luck and Have Fun.

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