Typically, you want to cruise around the fat of your tq peak. The reason for that is because it takes less effort to move the vehicle at the same pace. My tq peak starts around 3k rpm, which for me is around 60mph so when I cruise, I typically cruise around 60-65 mph. On the same token, the higher your RPM's are, the more fuel you're going to burn due to the fact that at higher RPM's the computer is gonna add more fuel to keep it from overheating from "leaning out". I hope that gave you your answer.