In a similar vein, if 2 engines good, 4 engines bad, how come the MD11F never really made it in the market (3 engines being somewhere in between good and bad...
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There were a number of reasons for the MDC buyout but shutting down the MD11F was certainly a big one. The 777 could not compete at the time (they did not even want to try) and the 744F trailed behind in pound per mile/fuel burn.
The MD-11 became a better option when markets receded, ATLAS just about tanked with a whole fleet of 747's in a slow market.
The 748f will probably be more efficient than the currently being produced 777f that is based on the 777LR. Boeing added alot of composite structure to the LR as I understand to make it a competative aircraft.
We must also take into account the difference betwen the value of bulking out v/s weighing out an aircraft. A 4 engine bird will allways be valuable with weight in mind. Package companies will probably do well with the 777F as the rarely take off at max gross but the aircraft has volume. The 748-F is sure to be a great heavylift aircraft.
Another aspect of the industry that the 747 and 380 are an asset in are regulated markts. If you are only allowed x amount of slots at an airport but have lots of product (pax/freight) you can maximize revenue by having a larger aircraft.
Back on the main topic, these aircraft if 7R4 powered should be quite marketable. I too have never seen a 7R4 on a -200 but it is a great improvement over the pain in the ass -70.