I don't understand the reasoning behind your question.
No hybrid is the "right hybrid" for 70 to 75 miles per hour.
All hybrids will go that fast and all cars, hybrids or regular, will get worse MPG at those higher speeds.

A hybrid WILL give you better MPG than a regular car at any speed.

The 2006 HCH is an excellent car.

Sometimes I read that the Prius is better for the city and the HCH is better for the highway; I think that is hogwash.
MPG is sooooooo much more dependent on HOW you drive, than on which you drive.

You wrote that 60 miles per hour is the sweet spot.
If you mean the best MPG, I think the best MPG is closer to 45 miles per hour.
The faster you go that worse it gets.

As to what MPG to expect at 70 to 75 miles per hour, I can't say as I never go that fast.
But I'd say you may range from 35 to 50 MPG depending on your willingness to learn and apply the many tips and techniques for effecient driving and your driving conditions and weather.

This is MUCH better MPG than a non-hybrid.

Need fewer troops to support.
Drive a hybrid.
Best tank 71.65 MPG.

Before this car I spent two years learning hypermiling on my 2004 HCH1.