Even if GF ordered the planes (assume 787's), it will be till 2010-2011 before they get them. If they order A350's, even later (2012-2013). Unless of course they find a way to lease some 330's from someone (at a hefty price).
As for the two types of aircraft they intent to have, that is a tough question. GF needs three types in total in my humble view. Two types of long-haul aircraft esp. for routes in which cargo plays an important part in route profitability, and another type for short hauls. The A330 cannot make it to Manilla (just one example) unless it is weight restricted (hence it uses 340's). GF could loose a lot of money reducing its A340 passenger capacity to particular markets (such as LON and FRA) to that of the A330 esp. during peak months of travel.
It will be interesting.