We pretty much already saw how this fight went down minus the Rinnegan, so Minato without any distractions could more than likely take him out. We saw how he stole the Kyuubi away from him with his sealing jutsu, and Minato being a master tactitian he could figure out the strengths and weaknesses of the Rinnegan, also something to point out, we haven't even seen Obito use his Rinnegan that i can recall...sooo yeahhhh..
+1 Minato