The problem when you compare an airplane's range and geographic distance is that you don't take winds into account. "Still air distance" is a physical representation of the impact of winds on the flight time, ie. the actual distance with winds = the virtual still-air distance.
On the LAX-SIN route, that gives you an idea about how wrong one could be by comparing actual distances and range performance without taking winds into account. So, the 777-200LR and A340-500 can fly the SIN-LAX-SIN sectors year-round but with about ~200 seats. There's absolutely no way these airplanes could fly JFK-SIN non-stop (unless you remove all seats, don't paid the aircraft, ...).
SIA's requirement for the LAX-SIN route has probably been the most serious one (as compared to JFK-HKG or PER-LHR for instance). But this sector has given both manufacturers a hell of hard times. This is clearly outlined in my Boeing 777X
article. The 747-400X, ER & QLR
] has a paragraph on how Boeing tried to make a case at SIA with its 747-400ER and -400XQLR, arguing that the airline could have a load of nearly 250 passengers and thus be less dependent on high-yield traffic.
AFAIK, the second route slated to get A340-500s is SIN-SFO.
SIA not ordering the 777-200LR because of its GE90 powerplant is clearly not a valid argument. The airline along with MAS, wanted an airplane that would meet its requirements, whatever the powerplant. I have multiple developments on this in the Boeing 777X
] and General Electric GE90
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Photo © Andrew Hunt
ATB - Boeing 777X