It would be a close fight. But what counter does Nagato have to TBB+Sand Tsunami? If he tries to absorb that TBB he'll get suffocated by sand especially if it's in a desert. Nagato's summons would cause some trouble, and Gaara's TBB's could destroy the CT's.
Plus Perfect Jin Gaara would for sure have Futon: Sand Scattering Bullets which even Madara couldn't dodge, which could allow Gaara to immobilize Nagato allowing for the sealing Gaara attempted on Madara (the pyramid thing but with Shukaku's seal)
So Gaara mid-high-diff at most in this scenario.
Without a desert, Gaara extremely high diff.