I got out on the highway with the cardboard mods the other day, and I think they helped. I was getting about 19mpg with the fairing on, before the tape started to fail.
I stopped, pulled off the fairings (carefully enough to avoid damaging them) and got back on the road. I resumed the cruise control at the same speed (about 135km/h) and was getting between 16.5 and 17. Not an A-B-A controlled test, but the road stays level (actually slightly uphill as it follows the river) and the wind wasn't blowing, so I think it's indicative, if not definitive.
I know, it's a shocking waste of fermented dinosaur blood, but I was in a hurry to get to an interview. And I made it with one minute to spare. I drove 60 mph all the way home to make up for it.
