When you say Pain, do you mean Nagato? If so Nagato is way stronger than Itachi?
Nope, Nagato. I stand by it. I've read the fights and thought about it over and over again and they're pretty much equals, but what gives Itachi the edge over Nagato is Totsuka Sword, Yata Mirror and Itachi's smarts - the ability to identify weaknesses and make a strategy to defeat the enemy given the powers, equipment he can use. I guess that is more about who can/will beat who, and even then it can go either way. But even in terms of power matching, I still find Itachi somewhat dominant in terms of the superiority of the power of some of the ability he possesses and the skill he can use them with - I'm talking about Izanagi & Kotoamatsukami here.
In terms of Raw power... Yes Nagato >>>>>>>>>>>>> Itachi. But power in general, Izanagi & Kotoamatsukami - which is available to match Itachi are overhaxxed abilities that match Nagato's most haxxed abilities and exceed them. I've always found Izanagi, Kotoamatsukami, Totsuka Sword & Yata Mirror combo too haxxed as they actually mess with reality, which I find more dangerous than disintegrating whole villages to dust. (Sounds backwards, I know).
Nevertheless, Izanagi & Kotoamatsukami would be moves Itachi would/could never use unless his motives in the manga/life were different (i.e. he didn't want to give Sasuke his eyes).
