Driving at 60-70mph drives me nuts. At 60mph, you're constantly looking for the gap to pull out from behind the truck doing 55, at 70 your constantly looking for the gap to get out from behind the middle lane hog, I find that at 80 on clear-ish motorways, I tend to not have to vary speed or change lane very often.
Obviously, when it's busier time or area, speed tends to be closer to 60 and that's fine. I'm not a speed merchant, just really wondered how much range penalty is payable for the extra 10mph