Actually the A330-300 that Virgin have ordered is not operated by any other British operators, across the Atlantic or elsewhere. A number of the minor British companies do have the A330-200, a notably shorter and different aircraft. The nearest you get to an A330-300 Transatlantic fleet is the Aer Lingus one. However in the time since they built up this fleet (Aer Lingus were an early adopter of the type in the early 1990s) it has been steadily developed in capability.
Thread drift....Just as an aside I think you'll find Thomas Cook have a -300 in the fleet this summer.....with a couple more in scandananandavia.
& what do you mean by capability? Maybe a couple of tonnes MTOW but otherwise same range of engines + same tanks = same difference bar electric rudders and fancy screens etc
Good move for Virgin - mixed fleet flying 340/330 will help costs, crewing and more choice of routes for the drivers