Suspension real vs GT differences
I noticed that raising and lowering ride height has no effect on shock stroke. If the car is lowered the ext stroke remains the same and the wheels will ext the same amount, this can be seen when making a jump, the lower the ride height the less drop the wheels will have when air born. If you raise the ride height the wheels drop lower. The compression stroke only gets reduced when the body is dropped so low there is not enough shock travel for the shock to fully compress. The travel is 2/part, first how much travel the shock uses, and second is the body travel limits limiting the shock travel required.
This would suggest the body is simply being lowered and raised when ride height is adjusted and the suspension remains fixed. In real life raising ride height increases comp stroke at the cost of ext stroke, while lowering ride height cost comp stroke to the gain of ext stroke. In GT we only need to consider body travel limits, we don't have to think about ride height adjustments affect on comp and ext stroke as we would in a real car.
I also notice all cars seem to have similar geometry. While some cars have more or less overall wheel travel distance than others (seen in data logger) they all have the same amount of camber gain inside the range of travel. No matter what kind of suspension the car is supposed to have, all cars appear to have this same geometry, no live axles, no double wishbone or trailing arms, all cars have a simple fully independent suspension, with the same camber gain.. There is definitely a variation in spring rate to wheel ratio, but it appears to be nothing more than an amount of "leverage" calculated.
Body travel
While greatly improved over GT5, the body roll and pitch is very basic. Where in real life there is increased angle and more pivot at the limit. In GT pitch appears to have a small level of pivot the roll does not. If put in an extreme situation like bouncing off a curb, there is no real pivot on roll, and as soon as an active force lifts a tire off the road, the other side digs in like a anchor and sends the car rolling. It appears as if rolling over onto the tire side wall is the limit of the simulations abilities. This makes tuning cornering performance frustrating, the suspension is too "perfect" and the tires only well simulated inside a window that falls under the limits.