The 77W has the legs westbound, especially for this time of year. I am actually a little surprised SQ never attempted SFO-SIN with a 77W given their low density of 264 seats. CX, once upon a time, was flying EWR-HKG with their 368 seat 77W. UA ordered the 77W, with the final PIP offered by Boeing which increased its range slightly, specifically so it could operate EWR-HKG with 360 seats. That was before Premium Plus was introduced.