Both routes would require ( beside getting the traffic rights , ask SQ on OZ-USA ) a 772ER or A 345 ( SA is doing the JNB-ATL route with a 345 )

Sticker price of those birdies is close to $ 200 million, the Airbus is cheaper, but more costly to operate.What is better for an airline may come down to accounting and the market conditions how to get a loan / or leasing conditions.

If you fly a subfleet of a handful of aircrafts it is already not profitable anymore in most cases...