I just found this posting by a current A340 pilot on another forum. I thought I’d repost it here for interest.

‘The A340-300 does not fly lower than other airliners; in fact, it is usually a little higher – at least in the early part of a longhaul route. At M0.82, it flies a little slower than the B747 (M0.855), thanks to the less swept wing. The A340-600 shares most of the wing with the -300, but cruises a little faster (M0.83) – and will get to cruise altitude faster than either the A343 or the B744 at typical commercial weights. Neither A340 can cruise at the Boeings FL450 maximum, but their cruise maximum of FL410 is sufficient for most radiation-aware pilots.’

The implication from this is that the extra fuel the 744 has to carry due to being less efficient causes it to be unable to achieve more efficient levels until a later stage than the 340. In time however its performance will allow it to climb higher than the 340 if there is an advantage in so doing.