Since not many people take their cars up to top speed the experiences are far and between. Here is what I have experienced in top speed runs.
1. In some cases when I was running pump gas (I didn't have the logger on during the times it happened) the car while accelerating from anywhere between 150km/h and 240km/h would like you mentioned hit a wall but in my case it is brief (1-2 seconds) and then the car continues to accelerate. Having said this, I have not had this issue occur again since moving to 100octane fuel.
2. The stock mapping has a top speed limiter that kicks in at 221 km/h and I had posted about this before (see link below)
http://www.ft86club.com/forums/showthread.php?t=58835
3. Friends of mine with ECUtek have had issues with top speed that are a bit different. In their case the car hits a wall at 210 km/h every time without fail.