You say 641 for your prediction,the way Kishi works is in 5 and 10 when something big happens. This last chapter was 640 and Obito's taking control was set up by chapter 639 when the Juubi body was changing shape.If Obito is about to be defeated it be set up in chapter 644 at it end so that Chapter 645 you get the impact. I am sure just before Naruto defeats Obito we will see Obito tacking about that weird felling He gets about Naruto power,its happen before after Naruto learn the names. And power ups after that Obito could not explain the weird sensation He gets from Naruto. So look for Obito getting that weird felling but stronger before Naruto defeats Him.