Is Ducted fan or Propeller better to maximize forward speed of RC aircraft with a given power? I'm designing an RC aircraft of which the final goal is a crazy top speed. I'll be 3D printing and sanding / finishing the air frame surfaces to reduce drag. In order to achieve maximum top speed, should I use open 5 inch diameter 3 blade props (the ones used in racing drones) with a large pitch and beefy motor, or two (60-80mm) ducted fan (EDF) units? Power draw is not a limiting factor here. Also, should I go for a larger EDF than 80mm? (wingspan is about 70 - 80 cm, total mass of about 700-1000g) . I'm aware that EDFs induce a greater delta V on the air they move, but does this actually mean I can expect a larger top speed?
[edit:] I could also go for a single 100mm unit.
A propeller is better. Just look at any pylon race model to see what they use.
DKNguyen put it very nicely:

A duct doesn't beat a larger prop, it only helps make up for a smaller one.

You're right that &quot;EDFs induce a greater delta V on the air they move&quot; but EDF models generally use twice as much power as a similar aircraft with a prop. Moving half as much air twice as fast generates the same thrust but requires twice as much power. This is because momentum is mass x speed, but energy is mass x speed squared.
Ducts (and multi-blade propellers) are used when you don't have space for the right sized prop for the engine power.