Well, I would guess that Joyce has a better chin than Wilder. And against Zhang, Joyce wasn't around after 5-6 rounds. So who knows if it'll go past 5 or 6.
I suspect the right hand of Wilder, which is the perfect weapon against a southpaw could KO Zhang but then again Zhang ate a ton of right hands off Hrgovic who isn't exactly feather fisted. Comes down to how Zhang takes the shot, if he can take it like Fury did then Wilder is going to have to come up with a bunch of all new excuses to why he got his ass kicked. But lets be honest, no way in the world Wilder would ever take such a dangerous opponent on. Haymon would have to sign Zhang first, wait until he ages out and shows some sign of deterioration and only they maybe do they make the fight.
A war, if Fury can drop Wilder, why can't Zhang. I t will ultimately come down to if Wilder can survive the early rounds and find the mark with his right. I personally favour him to stop Zhang but not until after some tense moments.
If Zhang didn't win by knockout quickly, he would be in real trouble. Fury is certainly more mobile than Zhang, and has better stamina (and Wilder has better stamina) than Zhang. How would Zhang behave after being punished this much: This content is protected That would be an opportunity to really test Zhang's chin, and if he doesn't have a chin like and/or a recovery like Fury's... good night.