Thing is your ECU gets used to the fuel you use, so putting a tank of super every once and while doesn't help, unless you put in 2-3 in a row. Then if you fill the car back up with petrol it will take another 2-3 to get used to that.
Better off sticking to one or the other, unleaded in the normal engines super in the ///Ms
Although if you do put Super in the car will feel marginally more responsive and may give you 1-2mpg more.