The "system" of can control, says that you should select a grea "before" completing the overtake.
That gear should be sufficient enough for you to be able to overtake the vehicle, then after you have passed the vehicle change gear.
You don't change year when alongside of a vehicle !!
In a manual, cruising at 5th or 6th .... depending at what speed your doing of course, but suggesting that you are sticking to the legal limit, on a national ... i'd say 3rd gear would be sufficient to complete to overtake, then pick gear 4 when the overtake is complete.
With an auto, i've got an auto ... and yes it does have kick down ..... if you select D3, that just means the car will stay in a top gear of 3, and there for won't choose 4.
So if you flick it over to D3, before doing the over take, then use your kick down pedal to overtake the vehicle ... once that's complete you can flick it back over to D4 to change gear, and give the reves a chance to breath.
Trust me :-)