Looking at the turnaround times at ARN :

BA776 1105 1220 (1:15)
BA774 1355 1540 (1:45)
BA778 1500 1655 (1:55)
BA780 1655 1810 (1:15)
BA782 2025 2105 (0:50)

you would presume it would take longer to turn around a 787 than an Airbus, and that BA would pick a rotation with some slack in the turnaround time to avoid affecting punctuality while teething issues are being dealt with.

My money would be on the 774 and 778.....