Personally i use Fuchs Titan Race Pro S 5W-40 Ester Synthetic Engine Oil from opie oils
6 litres does it with a bit to top up,Use a good quality filter also.
Motul 300V Power 5W-40 if you want the very best but expensive at £105 for 6 litres!
Don't stick to factory intervals for the sake of your dephaser.just stick to factory recommendations IMO.
Personally i have changed my oil and filter every 6K since new,some may say its overkill but good lubrication leads to a healthy long lived engine.