If you study history of aviation really carefully this is not quite true. But I agree that the "absolutely" fastest is not likely to be a pusher (for various reasons ), but most economical it could be.

1. New Avanti Piaggio goes 740 km/h (name a faster turbo prop passenger craft )
2. Learfan 2100 was more economical and faster than Citation I Bizjet
3. Mixmaster did the same as B-17 but with 2 engines and was 100 mph faster
4. Edson Fessenden Gallaudet flew 130 mph in 1912 with a pusher.

I could also mention that Lars Giertz whose VMax Probe was demolished in testflite mentioned his plane could go(calculated estimate )240 mph at 50 hp and was after 300 mph at 80 hp.

I do appreciate your input..there is lotsa variables to consider. Also the Molt Taylor dream of a really economical pusher Micro Imp never realised it became 240 kilo plane. Jerry Holcomb was able make a one (Perigee )at 166 kg.

I think to accelerate the flow at fuse and reduce drag the fuse would have to be really clean and the turbulent air to the prop would have to come somehow projected evenly pressurewise...you know what I mean ? This is why I have the wing throwing the "turbulence" middle of the prop arch in my MAX III. The fan/prop would then have to deal with this wash as efficiently as possible. new ellipse prop for instance could have an answer.

I think the biggest obstacle in pusher systems so far is the cooling and maintenance of the engine. (Second is the CG management..they tend to be tail heavy ).

More about my pusher here: http://max3fan.blogspot.com