MarkD as you said,
"as was pointed out, the CFMs are there for frugality rather than puff!"
And to an extent so are the climb profiles. You could probably get the 340-300 to altitude (lower levels anyway) a bit faster than a lot of operators currently do, but at the expense of some down track distance. The whole thing is cost in the end. If the profile at the higher altitudes is more of a cruise climb than a sprint to cruising level it may well be more economical.