I think this example shows more that the difference between vagueness and simplicity is dependent on the context. If I talk to somebody who has not read LW/rationality/IQ studies they have no concrete mental model of what it means to have IQ 130 (other than that the higher IQs are better). So then saying “you need IQ 130” and explaining in a convoluted way what exactly did you mean by that conveys less information than just saying “you need to be smart” and makes a simple statement more complex.
On the other hand, if I talk to somebody about whom I have reasonable expectation that they understand what the IQ actually means, saying smart is also simpler, but due to the abundant and less well-defined use outside precise conversations, it might make sense to default to more precise and quantitative statements to avoid confusion.
One more thing to consider is where you would be driving. I would guess that if you drove in urban areas where speed limits are about or below 50 kph (30 mph?) your risk of death while driving within speed limit is much lower. Also, using seat belt appears to be pretty useful (40+% of fatally injured occupants were unbelted). And when you would be driving is also somewhat significant (though I assume the dependence on time is at least partly caused by there being relatively more drunk drivers during weekends and nights)