It's pretty bad. Looking at longhaul (block > 8h) flights from June 1 (when longhaul 77W got going with some volume) through last Sunday, it's the worst active widebody in the fleet for A14. By A60, which I sometimes argue is more relevant for longhaul than A14, it's worse than the 772 and all 787s.
Code:
aircrafttype | a14 | a60
--------------+--------+--------
B744 | 63.7% | 88.0%
B763 | 83.5% | 92.4%
B764 | 84.2% | 92.9%
B772 | 81.5% | 94.7%
B77W | 76.8% | 93.8%
B788 | 81.6% | 94.2%
B789 | 79.7% | 94.4%