Do you even have a drivers' license? You evince very little familiarity with practical every day driving. If you are a driver, how many years experience in which countries? It would help us gauge the relevance of your comments -- different countries have different driving cultures.
I also often find myself driving among other people who speed. I stay to the right with the OTHER drivers who are following the law. I always drive the speed limit and it's never a problem for me. Many states' laws require this, anyway (faster traffic to the left, slower traffic to the right).
But if the prevailing speed feels safe -- it might just be 5 MPH over the limit, or the limit might be unnecessarily low -- of course I will just go the prevailing speed, to maximize safety. What kind of a fool would do otherwise, just to satisfy an imaginary policeman in his head?
But trust me, the imaginary police are very much not imaginary. I got a couple speeding tickets before I decided I wasn't going to deal with the courts ever again. Now, I do the speed limit. I see cops everywhere on the highways in my state and they definitely will pull you over going 10-ish over. Until recently, anything over 80mph (even if the highway was posted 70mph) was reckless driving (now It's 85 I think)
Hold on now, that's just an opinion. And while it happens to kind of match mine, everyone's opinion on how much speeding is "really speeding" is kind of different, up to a point. Kind of proves my point-- I don't want something stopping me from doing 5MPH or 10MPH or even 15MPH over the limit if circumstances outside of my control indicate I should (NYC is a good example of an area where EVERYONE going 15mph over the limit is not unusual)
My personal rule of thumb is to make sure at any given time, considering yourself and the drivers near you in view on the highway, that you are either under the speed limit or at or below the average speed everyone else is going.
If everyone else is going 10 MPH above, go 8 MPH above. As long as most drivers near you are faster, a cop will pull one of them over first. Never go above the speed limit without a "Speeding Buddy" (a driver who is going even faster who is a few car lengths in front of you). If you have no Speeding Buddy, you don't need to speed, you can just go the speed limit.
Also, the speed limit isn't 55 in the US. It varies between 50 and 80 depending on your state and region.
See, and I was taught 10 mph lower, and that has been my experience driving in many states—8 mph over and you're fine, but much higher than that and you'll get pulled over.
Driving 65 in that situation makes you the bad guy. You may literally cause deaths. Blind obedience to authority is not a virtue.