The 340 does Far East (narita, shanghai, hong kong/sydney rotation) and the west coast US (shared with the boeing - LA, Vegas, San fran). It also does various New york rotations and also cape town, Joburg, lagos. the 330 changes seasonly. Mainly Caribbean, indias and Dubai in the winter with some New yorks and more east coast US and Chicago in the summer. I think thats fairly accurate.
If you download the virgin app then you can see which flights are flown by which aircraft.