Your right, Caymen, time is money. But in your example, more time spent traveling meant more money earned (more cost to your employer, sure).
There have been tons of studies. "Back of the envelope" calculations are often misleading. Most of the studies show that dropping the speed limit from 65 to 55, or even changing your driving habits to the same degree "can" save fuel and money without having a big impact in your time.
I am not an advocate one way or the other, but I just caution that overly simplistic analysis and statistics (used on either side of the debate) can be misleading.
Setting the speed limit to 80, on most roads in this nation is a bad idea, IMHO. I fear that most of the roads and the average skill of the drivers on them makes for an unsafe combination at such high speeds.
Oh, one last thing, Caymen, you seem to like equations and want to speed so that you have more time to do the things that make you happy. Consider this:
o Time = Money
o Money Cannot Buy Happiness
Therefore, by the transitive property additional time gained from speeding can't make you happy.
TJR