IMO Korobov beats Lee pretty clearly even with his tendancy to take rounds off. Korobov is highly skilled, with good power and a decent chin. He's undefeated and will be a titlist. What would this win do for GGG's resume? best win so far? I suppose it depends on Korobov's career projection after the fight really.
Korobov is dangerous early, very talented boxer with quick combinations and superior power and then he gasses out around the fourth round. GGG is a complete fighter with no weaknesses and takes over the fight after 4 or 5 rounds of tense boxing. I would pay to see that fight, both gifted amateur boxers with great pedigree.
He didn't gas going 9 before stopping Edwards and while he looked to take 2 or 3 rounds off against Uzcategui he finished strong. Even when he is tired his technique isn't compromised his output just drops, against most fighters it wouldn't be much of an issue aside from possibly losing the rounds by getting outworked but against GGG it could cost him worse. If he looks good beating Lee it could be on par with the Geale win (unified champ) but ultimately better because he's a more formidable stylistic matchup.