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.
FocusFest 2013: Best of Show
Gateway FFW: Show Class Outstanding
September '13 ROTM
Hatch Nation #161