Nadal's chances to catch Federer probably died at Wimbledon this year. Had he won he would only be 4 behind now and would have a real shot, but 6 behind and with all his momentum gone with the combination of a terrible Wimbledon and injury, it will be extremely difficult. I think it is looking more likely the order will stay as it is now. Nadal probably wont catch Federer, Djokovic probably wont catch Nadal, Murray IMO definitely wont catch Djokovic (even if he is the best and most successful player and wins the most slams of all over the next 4-5 years which I dont think will happen, he still wouldnt be 4 or more slams better than Djokovic in that span). Lastly Murray will definitely win more future slams than Del Potro. In a sense I hope Del Potro reaches 2 or 3, but in another sense that would be an injustice, if he does it he deserves it, but looking at players like Roddick and Hewitt who stayed at the top level for so many years and only won 2 or 1, Del Potro doesnt seem worthy of anymore than 1 by comparision.