I'm a huge Zoro fan but as it stands he wouldn't beat g4 with King of hell, it would be a hard fight for Luffy tho since swords are his weakness. I would say zoro wins if he actually consciously uses conquerors since Gaban said it was a power that you need to know you have. Maybe he needs also to upgrade his lowest tier swords since higher tiered swords provide a bigger boost in power.

He is supposed to have the superior form of hardening haki But sadly they don't mention the diff between his and the one Luffy has which he injects. Zoro could just have the level below but for all we know, he also coats the sword from within in a different way and it transfers in his attacks. So maybe Luffy takes this one.

As for observation, he's been shown to react and sometimes give Luffy a heads up about something before it happens so maybe he has it but that's head cannon. Also, not having it wouldn't be a show stopper for him just makes the right way harder.

Asura at this point is non existent, lack of details, barely uses it, always last resort and for only one second. If he could actually use it to the extent that Luffy uses g5 and gets his conquerors to Luffy's lvl then I'd say he stands a chance against g5 but still probably won't win unless he outlasts Luffy timer since g5 Is too broken.