My assumption is that most of the folks posting here about speeds below 65 MPH don't drive in the West.
Speed limits where we travel are 75 MPH as well. Sometimes 80 MPH. I usually set cruise at 70 MPH. Sometimes 75. And, at those speeds, I rarely pass another RV. But I have a ton of them pass me. Especially if I am at 70 MPH.
I am also in the camp if you are traveling under 65 MPH in the West with speed limits of 75 - 80 you are impeding traffic, and it would be safer for everyone if you chose routes off the interstate.