There is no "flow of traffic". Not with speed-governed big trucks where their limit is anywhere from equal, to as much as 20-mph below the road limit. While a few firms have their trucks at 62-mph, most are at 65-mph. And only a few above that.
And the four-wheelers jammed together at the limit for the road.
Granted, not all trucks are governed. It the above should be a guideline to Interstate speed. Run 62-mph and there'll be no lane changes or last moment braking. Peripheral vision is still quite good, and just maybe a well-maintained rig can stop reasonably well.
Running above the limit of the trucks is illusion of speed. A great deal more effort and constant problems with maintaining a 700' space ahead. Even 300'. Reward doesn't equal risk.
Know how to identify a stupid RV'er? He's the one surrounded by other vehicles. Lacks the minimal mental horsepower to back out of these situations.
Do the math. Engine run time per hour meter divided into miles. The difference between the 62-mph and 68-mph is negligible. But all other factors (economy, tire and brake life, diminished driver skill) are better.
A solo pickup can't brake worth beans above 65. And given the possibility of jackknife, towing this fast isn't the mark of intelligence. Quite the opposite.
I run over 10,000-miles monthly. It's only about every couple of months I see a solo vehicle operated without mistake. Anyone care to guess how many thousands of vehicles that comprises?
Plan the trip by planning the stops. And their duration. Run the trip as a series of legs. This is how to "save time". It isn't done by increasing risk for no gain.
About the only way to make a high AVERAGE mph is to both leave and stop early. All over the country traffic ramps up by noon and does not dissipate by midnight.
Dark o'clock early departure works. Ironically (yet logically) a slower travel speed with this approach trumps a higher one late in the day.