I doubt you're gonna read all this, but whatever
Yeah Nick can't make 155 though. Even if he could, his cardio would still be fine like it always is/was and Conor's will likely still be the same, unfortunately. He weighed in at like 154 against Floyd (gained weight back, of course, everybody does, especially Conor) and still gassed in the same amount of time against Floyd as he did against Nate pretty much. Conor had clearly slowed down considerably about 12 minutes or so into the fight against Floyd, just like he did against Nate in the rematch at 170. The thing about Conor is that his style and body type isn't the best when it comes to conserving energy.
He fought at a lower pace in the rematch against Nate early on, but still gassed badly throughout the 2nd and 3rd. He's a fast twitch fighter, he's explosive, fighters like this aren't known for having great cardio but most people can barely ever bring them to that point because they usually finish their opponent before they get tired, which Conor does since he has finished basically every single person he has ever fought pretty early on besides Nate. Nate is the only guy that could push him past his usual limit. Nick would definitely do the same thing only it would be worse for Conor than what Nate did. Overall, Nick's boxing is better than Nate's. Some people like to say Nate is better, but he isn't.
Nate has a very good jab and straight left, a very good 'check hook' with his right hand, but Nick has so much more. Nick has much better combinations, he mixes it up 100x better with hooks, uppercuts, attacking the body, etc, as well as kicks. Nick also conserves energy better than Nate does. The way Nate actually slowed down against Conor in the rematch is something we would never see Nick do. We'd never see Nick throw continuous hard shots like Nate did when he swarmed Conor in the 2nd and 3rd rounds. He would stay measured and mix in heavier shots with weaker shots like he always does. Nate is very good at doing this, but Nick has delivered some of the most insane beatings this way for many, many years. The only time we've really seen Nate do this is against Cerrone when he threw hundreds of punches. Nick has made a career out of doing this.
At 155, I'd still take Nick because he won't gas out. He'd take Conor's best shots, come back and beat him up. It'd be like a bunch of his Strikeforce fights or the Gomi fight, or the Katsuya Inoue fight (only Conor would have way more success than Inoue did, lol). Stylistically, as I said, he's just a bad fight for Conor. I pick Conor to beat basically everybody he fights and I'm always cheering for him (except for when he fought Nate, of course), but I definitely wouldn't pick him against Nick. It's not because the Diaz bros are my all-time favourite fighters, but because he's just a bad match for Conor no matter where it takes place (weight class). I can see Conor winning a 3 round fight (even though I said earlier Nick via TKO within 3, I think it'd be more like round 4 TKO realistically), he can win rounds 1 and 2, lose round 3 and win 29-28, but he'd be finished in a 5 rounder for sure IMO. Nick's pressure, the volume, his cardio and even better chin than Nate's would be too much for Conor.
Conor truly is a better striker but his cardio would let him down. Conor, in my opinion, is currently the best striker in the game right now overall. He's just so fucking deadly. If he had 5 round cardio, he'd be unstoppable. He'd be undefeated right now in MMA in my opinion. That's what lets him down, it's his cardio, not his skill. Some will disagree with me saying he's the best striker in the game right now, but they can believe what ever they want. The way he outclasses such competition on the feet so easily is insane. The last person we saw beating guys that easily is Anderson in his prime. He makes people look like fucking amateurs. His countering ability both while moving backwards and forward in the middle of exchanges is the best in the game.
/rant