Check Airman,
You can't compare a B767 and a B747 because they are TOTALLY different
airplanes and even if they had the same power to weight ratio the performance wouldn't be the same.Many things like wing construction etc..
is playing a very big factor when it's about performance.
The 330 and 340 are almost the same aircraft , and they have the same
wing construction. What would the prestanda difference be if the aircraft
construction is the same and they had the same power to weight ratio??
Nothing i guess...