65ish mph. Sometimes if I am feeling crazy, I'll go to 68mph. My truck and trailer seem to like 68mph.
I do see a drop in mpg when hitting 70mph.
Right lane travel mostly, middle lane if available.
On local roads that I don't know, I follow the speed limit (or a little slower) even if locals are going faster. That way I don't get caught going into a turn or intersection area too fast.