Max MPG vs annoying other drivers

[Ferrigamo]

I have a non hybrid Honda Civic that has about 50k miles. Here is what I learned.

I can get up to 56 mpg going with the normal wind direction with about a 74 ft elevation drop from my driveway to work of about 48 miles. I have found that I need to be in Eco mode, I use enough gas to only have to moderately brake at an intersection, light acceleration and running 55mph on the highway, the temp needs to be above I think 50 degrees, not sure about humidity yet and I basically sit in the slow lane the whole way on cruise control. Going home the best has been about 46 mpg. I always use the base gas of 87. The quality of that gas also has a significant effect, say a max drop of about 6mpg.

The problem is that the speed limit is 70. If I go that fast, then mpg is about 42 with limited speed changes. At 55 mph, large trucks tend to run up close to me and are clearly annoyed. What are your thoughts on whether to drive slow or fast? My thoughts are that as long as they have a way to pass me and traffic is not too thick, then I will go slow.

Mike
Springfield, Ohio, USA