Rios is low no?
Murray ahead of Del Potro?
Rios: the list is purely slam based, Rios didn't do much at the slams.
Murray vs. del Potro: 0W-2F-2S-2Q vs. 1W-0F-1S-2Q. So it comes down to: is one GS (JMdP) title worth more than 2 (lost) finals and another semifinal (AM).
I guess this can be seen either way. There is a margin of error, certainly between #50 and #54.