Without going into too much detail...
Silk rope tends to be stronger than hempen rope. The exact strength of a rope is going to depend upon a lot of different factors including (but not limited to) the method of producing the rope, how many strands are used to make the rope, and the overall thickness of the rope. Silk tends to roughly twice as strong as a similarly sized hempen rope. That being said, both materials have strengths and weaknesses.
One of the main weaknesses of silk rope is that it tends to be very susceptible to abrasion. It also loses strength with time; while that is true of most any material, silk rope degrades quicker than many other materials do.