Nagato takes this. All the Gokage can do is feed him chakra due to Preta Path. Let Onoki be the first one to give him a load from Jinton, or the Raikage from his Lightning Armor. Bansho Tennin and Preta Path takes Tsunade down, she's a frail old woman without chakra.
Seriously, I don't see this being more than mid-difficulty for Nagato, as Hashirama was stated to make the Gokage's combined efforts look like nothing (implying low-difficulty) twice.