I've used Janes All The World's Aircraft for my figures.
I calculated the 340, 744 and 763 figures. Admittedly, I feel most confident with the 340.
For the 340, I think my number is fairer =)
The A340-300E option (used by SQ. Are they the only ones?), at 275,000kgs does use the CFM56-5C4 at 34,000lbs, but on their -300E a 5% thrust bump is available, which would mean a 35,700 output for 5mins.
So for 5mins, your power loading is 4.25. But at the standard 34,000lbs thrust, that goes to 4.39
But, the normal A340-300E (aka, -313X IIRC), has a MTOW of 271,000kgs, which is the figure I arrived for (4.33).
The CFM56-5C2 is only used on the -200/-300 (-311), which has a MTOW of 257,000kgs. If there's a good thing about Airbus, it's that their specifications are more standard, as opposed to Boeing's ones. Airbus has very consistent specs.
So, I suppose the anti A340 stalwarts can feel good about the A340s figures. But remember one thing, if you lose an engine on an A340, you actually have a better power loading than if you did so on a Boeing 777.
Thanks for your response, I'm closer to getting a good explanation. One day I will fly on a 757. Unfortunately, the closest thing I can get to a 757 in terms of power loading is the CRJ, but derate thrust and the fact its thrust is certified at only 0°C means that in real life, it's not as great. So for me, the A320 is still good fun.