Our concept of realistic is different. Realistic to me is a car in which human beings can realistically drive to their limit consistently.
Well that's an arbitrary definition. Whether something satisfies that or not has bearing on how realistic it is.
No human being could drive the X1 any where near it's limits on a real track surface.
Yes, no, and maybe.
A real X1 could have artificial caps on its performance to keep drivers safe or be driven on specially designed tracks to keep things in check. This could be as simple as taking it to an auto cross track where the speed might be limited to 100 mph.
Another thing to keep in mind is that the X1 in GT5 is a terrible car to use to judge the X1. GT5 has a bad physics engines. All the cars are ridiculous. The X1 apparently has an advantage over other cars in that it is sensitive to ground clearance and possibly weight transfer. For some reason, the F1 and X1 cars will automatically provide throttle when cornering and decelerating. It's either the simulation of a driver aid that's rendered pointless by the physics engine or a necessity to wipe out weight transfer effects that the physics engine could not deal with in cars like the F1/X1.
At 8G's you enter a corner and your arms will weigh more than your entire body. When you're braking your legs will weigh 250+ lbs each, so unless you are squatting 5 bills in the gym, you aren't going to be able to lift your leg off the brake.
Pilots deal with it all the time. If drivers don't want to it's as simple as programming a 6 g brake limit into the car's computers. Or not having a driver at all.
One imperfection, one mistake, one too many stones on the track, one mistake of a few inches on a curb and you'd be sucking the drivers remains off the track with a shop-vac. If it can't be driven to it's limits by humans, it's not realistic to me.
It's not realistic to you, but it could still be built, and it could be built and used safely. One mistake is all it takes to die in any car anyway.
Could you build the car? Of course. Can you drive it in a videogame? Yes, of course. If that's all it takes to be "realistic" for some, then I guess it's realistic, just not to me.
Well what else is realistic in a simulation besides something that behaves as it would if it were real?
If you want something unrealistic, it's probably unrealistic (not as in impossible, but as in improbable) to see X1's driving around the Nurburgring at full speed. But the same goes for F1 cars doing the same thing, but that's all over GT5 and no one cares. The reason why is because people [think they] understand F1 cars. They don't understand the X1 and go crazy over it when they don't even know how to tell if it's realistic or not.
Because a machine that can kill you in real life by just driving it is really real
You can show your calculations proving that X1 drivers would die automatically at any time.
You can also look up GLOC and how pilots get around it, or the effect of g forces on the body.