what is the kerb issue ?
I always find mad the ice feeling when you put a wheel on the green parts over kerbs ... but as I have never driven on a part like this in real ... I do not conclude
A part from this, I have a question for the experts : I find strange the difference in performance between cars of the GT3 'class' : yesterday I had a quick look to the mclaren and the mercs, and I find them more performant in corner than the nissan ... looks like tons of grip on the back. So they have 100hp less (are they really in the same class ? ), but they feel like having bigger rear tires, more grip on the front (iirc you can tune very slightly the front downforce, while on the nissan it is not the case ... it may be the answer). For example, I have used vallelunga club, and in the slowest corner, without TC, the nissan was very very difficult to avoid the spin, while the mclaren and the mercs : pedal to the metal without sweat (and again : yes there is 100hp less, but at 50-60km/h we are not at 8000rpm with full power) ...
So : is it realistic ? (nissan = beast, mercs and mclaren = baby beast, easier to drive in the end).
I had a quick look to the 458 gt2 ... but without ABS, unfortunately ... I will need more practice to finish a lap.
When you drive over a kerb the car kinda catches the direction of the kerb and you get a violent change of direction. Silverstone and mugello suffer from it more while others suffer less. Apparently cars can be adjusted to almost get rid of it by reducing damping and spring rate of the tire. The mazda 78787b does this really well and in that car you can use the kerbs fine but try to drive the z4 gt3 (I think) using the same line and you get those snap spins when the kerb snaps your car sideways.
That's pretty much how the GT3 balancing works in real life. The manufacturers come up with a car within a certain envelope and the FIA adjusts engine and ballast following tests. The Nissan is quite heavy and has relatively poor aero efficiency so I guess they are allowed more power.
The turbo lag doesn't help with the slow corner exits but it'll be strong in other areas...I can tell you it'll be on top of the GT3 class in AC at Spa. I'm matching reference times of the Z4, SLS, MP4 after driving it only for half an hour.