With the knowledge Orochimaru has about rinnegan chances are he would also know how to counter some of the rinnegans ability so I say he would have a decent chance of defeating 6POP (not Nagato himself, though) but not easily of course it would be a difficult match but I believe he would at least be able to do better than Jiraiya.
He was also the strongest of the 3 legendary ninjas and took on the 4 tails naruto (almost killed jiraiya) while his body was at its weakest.
http://naruto.wikia.com/wiki/Attack_...tion_Technique / http://126.96.36.199/manga/mangas/Nar...c171%20p06.jpg
this ^ is how he can evade chibaku tensei
http://naruto.wikia.com/wiki/Body_Shedding - this is how he can evade from anyone holding him like the absorbing path
http://naruto.wikia.com/wiki/Snakes - this is how he take cares of summoning path
One of Nagato/Pain's Realm can remove the soul of Orochimaru. Other than that, I don't see any other technique that an truly kill Orochimaru.
Lets not forget his staggeringly high chakra reserves and Unseen Forbidden Jutsu.