What calculator are you using ?
With a frameweight that heigh, and estimated total weight of 4 kg, I don’t think you will even reach 10 minutes flighttime, (without beating up your battery).
An X8 config doesn’t give your more than efficiency. On the contrary, it trades efficiency for thrust and ability to be compact.
The X8 config has a much higher discloading, as it moves air faster. To be efficient, you need to move a lot of air slowly instead. That means fewer but larger props.