The liquid is shielded in the wick from the gas and provides a return path. This pressure drop can be minimized if the pressure of the vapor is made high. The velocity of the gas moving in the pipe is inversely proportional to the pressure. A fluid that operates at a high pressure will have less pressure drop even though the flow is the same. The friction is controlled by the Reynolds number which is exponential.
Slower velocities are a good thing.
Even 5C is probably better than anything using ordinary conduction techniques. This tube was capable of acting as a temperature controller for photochemical baths. Ideally they would not be misible and had widely differing boiling points. This pipe purposely had 2 working fluids. This pipe had a resivoir at the top to contain the second vapor.