VS are quite happy with the -600s thank you. Some teething problems, as to be expected with a new type, but no show-stoppers so far. VS fit is 315 seats; as mentioned elsewhere cargo capacity is hugely more than 744 - the record so far, (that I'm aware of) is 38t - out of JNB, to boot.
Have not yet bothered to work out seat cost per mile, I'm not that bored, (or sad
) but an engineer told me the other day that it comes in well below the 744. Don't know how much he knows!
Operationally, in round numbers it cruises at .83, compared to the 343's .82, so is slightly faster than the 343 but slower than the 744. Fuel burns on the CLPs have been pretty accurate right from the start, (execpt at low level ie the last 200 miles to EWR!!), so I would assume that it is performing as promised.
As mentioned above, VS has never operated 342s, and the first 346 was delivered a little over 12 months ago - I think it was August last year, but my memory isn't so good any more! Sigh
Hope that helps.