There was a 2-yr period where Nunn was considered the P4P #3 behind Tyson and Chavez. He was FARRRR better and more talented than the Lemieux's, Macklin's, and Monroe's of the world. Golov has never beaten anybody as good as Frank Tate, Kalambay, or Barkley. Hell, even older Roldan is better than anyone Golov has faced. I know this forum is flooded with Golov groupies, but I'd actually take Nunn here.
I think I may go with Nunn here. He wasn't my favorite fighter to watch, but his outside fighting game and ranginess could certainly give Golovkin some problems who never faced a technician even close to this level..