Henry is right on the money. I used to fly internal combustion D/Fs that had 8lbs thrust on a good day. Manufactures used to spend a lot of R&D on internal ducting and airflow as these fans systems had a finite amount of thrust they could give, and any increase in efficiency resulted in better performance. The very top end Ducted fan jets were going over 230 mph with a D/F system that gave about 2/3 the thrust of a P60.

Nowadays if you want to go faster, the trend is to ignore airflow efficiencies, and just bolt in a big engine. Not really good engineering in my opinion.

Roger