As stated and as you know- add some weight up front and your problem is solved.
I drive 65 mph- if thats what the law provides for. If the law permits 80 mph then I drive 80-
PS- Driving below the speed limit is a real hazard so if you (this is directed to the folks that think life ends at 66 mph) aren't going to at least drive the speed limit you should stay off the highway! And for heavens sake- stay out of the fast lane unless you are passing someone. When you do pass, do it and don't spend 10 minutes. Be courteous and get out of the way.