Efficient car for higher speed cruising
 

What type of car would be efficient for high speed cruising, say 100mph, 160 km/h.

I know this is not entirely in the spirits of ecomodding/driving but sometimes it is just more economical to go fast. For example if you are many people in the car. Or in my case, if I can go fast and avoid rush hour traffic I can see a significant gain in mpg. Getting stuck in traffic sucks. And mpg goes up. (I once got 43l/100km. Going up hill for 2 hours at 3km/h) I could have walked that distance significantly faster. (I have started to bike to one of my workplaces 20-km one way 40 km round trip)
Sometimes blasting on the highway to go through a densely populated area at traffic free is an fe plus.

So, what would be a good candidate? A vw polo or a Passat variant have the same cdA of 0.66 so in this respect would they both get the same FE?

Aero mods would provide a significant advantage, also a gear swap if possible would make the most obvious advantages in my opinion.

Perhaps a motorcycle.

The Prius has a very low Cd and a variable gear ratio, so that would be my candidate in a car. If 2 seats were acceptable, the first gen Insight.

Generally any car that gets good efficiency at lower speeds will tend to outperform other cars at higher speeds.

No sense in making a purchasing decision based on this though unless driving 100 MPH is regularly done, in which case, I would buy something with a high safety rating.

I do ride a motorbike aswell. I have 3 of them. Unfortunately its not that easy to fit 3 people on one.

If I had such a luxury I would acquire a Volvo V70. Very safe, powerful, large, and fairly economical.it's a really nice car and I'll probably buy one one day. (Its on my car bucket list)
Around here a perfect condition V70 can be had for $5k-$8k.

I think a C class Benz with the 2.2 diesel would be the best, they even make a hybrid version. .24 Cd, not huge, don't know what the cdA is but must be pretty good with that .24 Cd.

You’ll subject the vehicle to a wear-rate not offset by putative fuel savings.

While it would not be ideal for the car to cruise at 100+mph (my Saturn gives me around 19mpg at that speed here in WV), you’d be best off with a diesel car(WV/Audi) that’s been streamlined as best as you can manage

Mercedes tends to have very low drag ratings on their cars. I'd probably avoid VW/Audi over reliability concerns. Given the choice, I'd pick a diesel over a gasser.

Other than that, look at Toyota's and Honda's hybrids, they have lower drag and this would slip through the air more easily.

I wonder if a streamlined C7 Corvette would do well enough cruising at 100? It might look weird with smooth wheel covers and grille blocking but I could imagine maybe 25mpg

I read somewhere that the 7th gen Civic gets 18 mpg with cruise control set at 110 mph. And that's with the stock drag coefficient. Not sure if it was manual vs. automatic or coupe vs. sedan.