I travel in the far right lane, and venture to the next left lane if the right one clogs up.

If the divided freeway has only two traveling lanes:
70MPH limit I'll go 65-68 with traffic, if there's nobody behind it will sag to lower 60's.
65MPH limit I'll go 62-65, same traffic rules as above.
55MPH limint is 55-62, same traffic rules.

Mind you I'll go faster in the valleys and low areas than at the top of hills.
If there is less traffic I'll let it sag more ove the hill tops.

I avoid +65MPH unless neccessary.

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT