Yesterday the weather was particularly hot (~90F). On my way to and from work, I pass a very flat stretch of road that's several miles long. I had to run some errands, so the car was fully warmed up, and coming home in the afternoon I noted my highest cruising mpg to-date:
125mpg at 50mph, sustained for close to 4 miles before the road became hilly again. I turned around and did two more passes to verify it was truly flat, and it was ~125mpg in both directions.
I did two more passes after that, one with the windows down, and another with the A/C on. Having the windows fully down did not show up on the FCD at all, which has 5mpg increments, suggesting the economy loss is less than 5%. Turning on the A/C instead, I found I was not able to get above ~75mpg (barely able to stay in lean burn) when the compressor was running. It blows very cold though and if I need to use it, once the system catches up I can keep the car comfortably around 68 with the compressor only running ~1/3 duty cycle.
My better trips lately have been ~95-100mpg, with a speed target of 50mph:
My average tank economy is ~75-80, because I share the car with my wife, and have been using it to pull a trailer a fair bit lately.