Originally Posted by dyn085
The DCT tends to get better mileage than the manual due to having near the same drivetrain losses as a manual because there is no torque converter to suck the power away.
I get an average 7.5 mpg increase after a reset with my driving style and route (from 26 to 33.5 mpg) when using 93 octane. I don't know but would assume the difference would be the same regardless of octane number. It takes me three to four full tanks to get that full increase and has happen three times nearly consecutively on this car.
The DCT gets better mileage due mainly to the taller 6th gear, as well as the fact that it is essentially a robotized manual transmission with a pair of clutch plates which hand off torque during the shifts. If the cars were similarly geared it might not have as much of an advantage depending on who was driving, how they drove, and how frequently shifting was needed or performed.