Great point Ame No Kage

Nagato has a stagegy formation for every opponent.He base a stategy just for jiraiya's uncertinty of the rinnagan and It ocular powers.That was no dought A pefect stategy played to percise fluency. The six pains see's all and they will see all of itachi's atacks.
Itachi will know this so Nagato will prepare. He knows when Itachi will use amaterasu and put Peta path there to absorb it.It is ninjutsu. Arv999 said that Itachi will go after Deva path but he is absoluty wong, he will go after Naraka path cus It can revive anything. Thats His Best Chance of defeating Nagato.His pain formation is designed for its protection. Nagato would Know that Itachi will try to seal Naraka path so nagato would make Animal path summon more Eyes on the battle field. He then would use Asura path to protect the eyes of any path and to counter Itachi's long rang jutsu. Nagato will get Human path behind Susanoo cus thats were it weakness is EVERY THING HAS A WEAKNESS and Human path is the fastest of the paths and specialives in taijutsu. It couldnt even be detected by the sensors in Pain Arc. He will make Deva path use Chibaku tensei and have Giant panda as a sacafice to the sealsword while he sends Giant Ox and Giant Rihno at susanoo
from each side to keep It occupide even though Susanoo cant destroy chibaku on his own. Nagato will test Its Yeta Mirror and close range combat hopefuly making an opening for Human path to get in close with Itachi. You cant deny the combos of the paths and its tech. No even counting the other 5 animal summoning and the way to use them.Nagato and Itachi Battle may have the most devestation off attacks clashing, but A HEALTHY NAGATO with pretty much unlimited chakra based on the 'Pain Arc' aginst A HEATHY ITACHI with a Stamina sucking MS cant beat Nagato.heaty Nagato can use deva strongest attacks More with little strain on his body.Deva path is best when fighting large objects like the 9 tails. Just like Susuno'o. AND THESE WAS JUST ONE WAY HE COULD DEFEAT ITACHI.
Im lazy when It comes to makin an case like this but it had to be done.