According to Wikipedia, Mt. Everest is 29,029 feet above MSL while the Puerto Rican Trench is 27,480 feet below MSL. The difference in height between the two is 56,509 feet or 10.7025 miles. The primary difference between the two is that people have stood on top of Mt. Everest, but no one has stood at the bottom of the Puerto Rican Trench.
BTW, the Challenger Deep is between 35,755 and 38,853 feet deep.