My "gut feeling" is that it probably takes more than twice as much space to stop if you double the vehicle's speed.
I think the fastest reaction time of people who aren't Chuck Yeager is about 30 milliseconds. At 90 miles per hour one is traveling at 132 feet per second. That means you travel about four feet before any hope of reaction. Not too bad for those who don't yak on the cell phone or ever tune the radio at that speed. Of course, the real trick is having the correct reaction. That is what separates the quick from the dead.
I've got to agree with you. Speeding can surely be a quick trip to the grave. Sadly, they are likely to take someone else with them or in their stead.
One thing that nobody can ever correctly anticipate is the reaction of the other drivers. The likelyhood that everyone will do the right thing at the outset of an accident is nil.
The most sorrowful thing that happened to me while driving 285 in Atlanta happened about twenty five years ago. I was a fairly heavy foot in those days, so I was going pretty fast. Some dope behind me was tailgating and trying in vain to switch lanes often to get ahead in really heavy traffic. He pulled behind me, turned on his lights, blew his horn, and followed really close. I had no way to pull over because I was already whizzing past traffic that was nearly stalled in the lanes to the left and right of me. Then I noticed that people in front of me were bailing out of my lane going left and right ... and in a flash it was my turn. Some extreme fool had stopped on the intestate in order to make a right he just missed. Using that last 30ms, I dodged left into a shoe-horn spot and braked like mad to merge in. The jackass behind me had no time to start his 30ms. I saw hoods, trunk lids, fenders, and windsheilds pass me. I never saw anything on the news, but I wouldn't be surprised to learn that everyone in both cars were killed.
Anyone who thinks they don't need that "one car length for every 10 mph" gap are stark-raving lunatics.