This right here is what defensive driving is supposed to look like. If you have the option to distance yourself from the other cars on the road, that’s always best.

It baffles me seeing a group of cars on the road all bunched up with less than a second between them going 75. If there’s a hazard on the road that the cars behind don’t see, they’re all going to crash into each other when the guy in front slams his brakes.

Driving is all about awareness and predicting what others might do. I just assume at any point, anyone could need to suddenly brake hard. Plan accordingly and position yourself defensively.

On 3+ lane highways, I find I can match the speed of a car in front of me with something like a 100yd/m gap. Faster traffic passes on the left. Eventually, I’m left with a fellow big spacer behind me. There will be a few of us big spacers all big spacin’ together, and it’s very easy for the Racin’ Randys to pass. In heavier traffic, I might see them anxiously tailgating in the left lane a bit ahead. Impatient drivers will break through somewhere behind us big spacers and zoom up to join the tailgating crew.

Rarely have to use my brakes, and can even make rare lane changes when HIGHLY optimal. Remember taking the same exit as a guy once who I saw change lanes a million times super aggressively half an hour earlier. I changed lanes maybe thrice. Wonder how our blood pressures differed that day - I know our arrival times didn’t.

Apologies for spreading potential misinformation, I too am having trouble finding a definitive source for what I thought was common knowledge.

I did some light research and was left with these notes:

• Air resistance increases at higher speeds by the inverse square law, more aerodynamic cars help offset the wind load but physics always wins.
• Peak engine efficiency is at the highest gear and approximately 1500 RPM, a more powerful engine may hit this at higher speeds.
• The EPA now tests various speeds up to 80 MPH when calculating highway fuel economy, so it wouldn’t be surprising to see manufacturers optimizing across the range.
• Cars that are optimized for the above points may get the best gas mileage at 60 MPH, but will have less MPG loss at slightly higher speeds.
• 90 MPH will never be more efficient.
• Personal anecdotal evidence has too many variables and I don’t have access to a variety of sports cars and straight level sections of highway with controllable wind settings to confirm.

I just posted an update under another comment asking for source information. TLDR: none.