There's no right and wrong answer, because every person will have a different experience.
Even with dyno tuning, variations in ambient air temperature and humidity, as well as altitude will affect mileage and performance.
Each person's driving habits are different as well. I've put 8,000 miles on my 2012, I'd guess probably 60% city and 40% highway. I've NEVER seen more than 35mpg, even on trips that were 100% highway, driving with the cruise control set the entire trip.
*I do have a heavy foot, so this is most likely my fault.
I tried 93 octane for 3 tanks of fuel and did NOT notice any improvement over 87.
After that, I switched back to 87 and removed the cover on the air intake.
Despite higher intake air temps, I did see an average gain of about 4mpg over 8 consecutive tanks of 87 octane, as well as better throttle response in the low end. Throttle response is better in the high end also, but not as dramatic a change as in low end. The engine stumbles less now as well, as long as I can get that stupid DCT transmission to downshift appropriately.
Next, I plan on trying another 3 tanks of 93 octane with the cover removed.