I also think 3-4-2 is the most sensible solution.
If there are very few passengers, then the 5 in 2-5-2
is ideal for stretching out.
Emirates manages to squeeze 3-4-3 into a 777...
Delta is converting its 777s from 2-5-2 to 3-3-3.
However, 2-4-2 is best seating configuration for economy.
(as in the Airbus A330/A340 family)

Just out of
curiosity, are there any airlines that manage to squeeze
2-5-2 into the A330 or A340?