Del Potro's best performance is actually probably not at the level of Murray's best on grass and maybe HC. Del Potro did play amazingly to win his Slam but he's always had limited movement. The top players learned how to consistently exploit that limitation to the extent where I don't even think a peaking del Potro with the fearsome forehand would typically have enough to counteract it. Murray has a less exploitable hole in his game if he's firing in full flow, that being the weaker second serve. His forehand isn't typically great but when the whole game is flowing it is a weapon. Both have peaks that are clearly below that of Federer, Nadal and Djokovic IMO. Safin's and Wawrinka's peaks are probably in the ballpark of those greats but they produce those peaks a lot less often.Although now that I think about it, I may be too in hock to the Safin/Hewitt paradigm. I think wawrinka did play better in his slam wins than Murray did in his, but I can't actually think of a del Potro performance that's better than Murray's best. His game is certainly more explosive but has he put on a better performance?