The car is not all that's at play here. Road surface quality is a huge factor. I've pushed a rental Merc past 180 km/h (110 mph) on a reasonably well-paved out

The car is not all that's at play here. Road surface quality is a huge factor. I've pushed a rental Merc past 180 km/h (110 mph) on a reasonably well-paved outback road, and it was downright unpleasant to drive at that speed from the vibration. On a smoother highway I would guess it'd still become unpleasant past 200 km/h (125 mph). Personally, I also found driving at those speeds too mentally taxing. The lack of time to react, the lack of maneuverability, and the huge braking distance were just too stressful. You couldn't let your thoughts, let alone your eyes, off the road for even a second. On that particular trip, I had driven for 18 hours (excluding short breaks and a 3-hour nap), most of it at ~100 km/h. If I had the option of driving 180 km/h the whole time and save 8 hours, I would not take it. That said, if there were no speed limits, I'd probably drive 130-150 km/h (80-95 mph), depending on the road, which isn't far from what volkk said.