Is the runway at Stansted realistically long enough? For the 788 at MTOW, sea level, standard pressure, it lists 2600M, and STN is 3049M. It's definitely doable, I'm just unsure on how much the weather will affect it.
JL flies the 789 -- which needs 2,800M at MTOW -- on the BOS-NRT route. The two longest runways at BOS are comparable in length to the runway at STN.