On my 2012 F30 335i:
Average daily high temperature is 108F
June 5 - 24.57
June 14 - 23.71
July 9 - 22.41
July 17 - 21.86
July 31 - 23.06
Mixed driving in Phoenix metropolitan area. 50% highway and 50% local roads. Most of the local roads are at 45mph speed limit and highways, I usually go at around 75-80mph.
My guess is that the efficiency will improve with cooler temperatures.