There is no such thing as a safe speed - even zero is unsafe sometimes.
The "risk" increases in proportion with speed but it also increases with conditions, road type, driver, pedestrians and congestion.
The big question is - do you know how good the other drivers on the road are? In the real world the answer is no. Do they know what to do when a car zips past them way above the speed limit? Again the answer is mostly no.
It may not be you that has an accident, it may not be anyone in the car that gets hurt but other drivers on the road are just as vulnerable and while they might be sticking to the legal limits they can be forced into an accident that seems unlikely and unexpected.
99% of driving fast on the road isn't what you are doing, it is what everyone else (not just the drivers) are doing. If you can't navigate those dangers without putting the other people out there in a compromised situation then don't drive fast - it is simple.
Accidents happen when something unexpected happens - the things you haven't planned for. The faster you are going the more it is going to hurt, cost, etc. So lets stop talking about being muppets on the road - if you want to do this sort of thing, either keep it to yourself or take it on to the track!