Not sure what speed has to do with it? As the saying goes the vessel to the right has the right away unless many things as Dave has mentioned. When you look at the vessel to the right, you will see the red nav. light (at night) this is like a stop sign. if you see green then you have the right away (approching the right side of a vessel. IF IN doubt ALWAYS stand down if it appears the other vessel is not paying attention or doesn't have a clue. What is ment by this is better to let someone pass then to crash because they don't know "Jack" about boating.
Common rule is sailboat under sail over power boat, power boats larger boat over smaller boats, It is primarly based on which boats have the most control and at what angle of approach each vessel is taking.