>> Preferred seating is for the front rows of the Y cabin only.
And the A380 upper deck Y cabin, which is definitely more important to me than where I sit a 35 min intra-Gulf hop (Al Maha substitutions apart ... ).
Choosing a B777 operated flight intra-Gulf is often good for op-ups when there is a down gauge, but less good if you've paid for J and want to avoid a cabin full of interlopers. I've had a pretty good success rate this year on B777 to A330 substitutions.