Hey, i have tested your handlings with keyboard.
Steering feels plausible for all cars. On decelerating the turn-circle is smaller, which makes sense.
The soft braking is great with keyboard. Makes sense for cars with anti-lock brakes.
I did not understand what you want to tell us with this menu graphic you have linked... is this meant as feedback guide or what shall be displayed?
The Vauxhall Monaro VXR drives very good. Pretty plausible for this car. But with this high g-transfer factor you will run into trouble with AI.
The Fiat drives good, has nervous rear which matches this car imo. But everything feels sluggish, it feels heavy and slow (im not talking about speed, but braking for example). Not sure if this matches this car. Rather looks like a small car (good braking and reactive handling), so handling is not plausible to me this way. Again high g-tranfer values will give trouble with AI.
The Zonda drives very plausible. Its my favorite from this handlings, but also brings the AI problems.
The Daytona, well, I know its the race version of the 69 Charger - but it simply drives too good for a muscle car in my oppinion
The car should have less grip and slower steering (if you go for realism). Also this car does not have antilock brakes. Of course in reality you dont slam the brakes full lock all the time, but it would be nice if the block after certain time (should be possible to set this behaviour with the brake increasing curve). This handling will also not work with AI.
Overall the handlings are very good imo. The biggest issue is that all of them break AI behavior. AI cars will always get stuck on slopes with g-transfer factor set this high. Maybe you can find a way to achieve similar handling with lower g-transfer factor (about 5.0 or lower)?