I just tried slowing down a bit and WOW, what a difference. Rural roads, a route I normally drive at 60-65, took it at 50-55 just for laughs and instead of ~ 47 I got 51.7 mpg. First 6 miles the lie o meter was reading 34.5 (hilly and city traffic), after 10 miles 47.4 and after 25 miles 51.7 mpg So on that last 15 mile stretch (some flat some hilly) I was probably in the mid to upper 50s, have not calculated it precisely. R/T today of about 100 miles including some trip on forest service dirt roads at 10-20 mph and a lot of up and down, average of 49 mpg. So I am seeing about an 8 percent improvement overall simply by going slower. I live a long way from the Interstate, and the speed limits are 50-55 anyway so slowing down is doable for me.
'013 SE, stock, fixed, DSG, 53,500 miles.
Update - repeated this experiment several times and the results are valid. On a rural road, fairly level (negligible elevation gain or loss), speed at a steady 50-55 mph, no wind, no traffic, I am right at 63.x mpg. I took a series of photos of my trip average mpg on the dash over 18 miles on the same trip to back up that result. Start driving in town - mileage drops like a rock. 42.9 overall mpg in mixed driving over the last 15,000 + miles. I do take a lot of short trips with a cold engine in town. That just kills mileage.
second update: Added a Kerma tune and seeing a ~4-6 percent boost in mileage.