I like this website for calculating RPMs and speed at a given RPM.
http://www.grimmjeeper.com/gears.html
Like others, I don't think I'd want to cruise at 60 for many reasons. I did see if my car with it's new engine could do it and yes, it can do 65 but I didn't keep it there more than 30 seconds.
In my rural area cruising at 50-55 is safely doable and my car seems perfectly happy to do it. That's about 2200-2400RPM.