See lots of differing opinions too.
Looks like one for Myth busters or an rockett scientist.
But I go both directions here and say it depends upon the vehicle, speed, grade, and length.
Ive traveled that same section plenty in the past with two distinctly different cars; first 84 SVO mustang with turbo and 5 speed.
It would climb effortlessly most of the way with no change in the R foot @70but there was a banking LH turn that always sent Turbo boost higher thus more fuel required or I could travel slower and get same reaction before that point and have more loaded engine time, diddnt matter which really never noticed true economy difference.
Second car was 71 Coupe Deville with HIPO built 500 CI and turbo 400 trans. This vehicle could cruise up 1/2 way @65 mph with a feather on the go pedal.
But still chug to top @55 when it dropped a gear still virtually unloaded.
But let someone stick that Caddi behing thier R/v and put it at 45 mph and It would Roar sucking the hood down in second the whole way up.
Unloaded rpms do best IMHO most cases.
Use your pedal to tell ya how much fuel your using I guess.