In Primera’s defence they are planning to use A321 NEOs with the 2 additional centre tanks. Why this thread title refers 320 NEOs I have no idea! According to Airbus, the 321s should make Europe to East Coast America (westbound) with realistic loads and winds. However, they may occasionally get caught out with stronger winds and capped levels when crossing which may involve having to reduce loads in anticipation pre departure.
When the 321 LR arrives in 2019, they plan to push the routes a little further.