I set my cruise for 80 mph when traveling, so I am on the same page. (I would drive faster but promised my wife I would not. Happy wife!)
The only reason I am focused on 75 mph and 70 mph results is because that is the speed independent testers are using. Using their test data is helpful when guessing what the Gravity will do. I wish they would test at 80 mph, but for whatever reason, they don't.
I want to go as far as possible on the highway. If it turns out the Gravity can't go 300 miles on the highway at a reasonable speed, it will significantly reduce the probability I will get one. I won't say for sure it is off the list, but I want range. As much as possible. (And something that will fit in my garage, because the long-range GM BEV offerings do not.)