@Icarus:
He isn't Admiral level quite yet, I would place him between Vice Admiral and Admiral now, how close to one or the other depends on which Admirals you use as examples.
I suspect he may have other new attacks too, just think, he could have used King Kong against Hody and the fight would have been over before it began or even against the ship Noah, but Oda did not write it that way for obvious plot reasons.
All Luffy needs to do is find a way to be more effecient with haki and remove the time limit for gear 4 and he will be set.
Must admit he needs to be more ruthless though when fighting he gives the enemies too much leeway and that is not a good idea in the new world, of course Oda writes it that way to keep the tension high I know but it is a bit of a glaring mistake sometimes especially when lives are on the line, I can live with not it though as it is needed for plot reasons.
Luffy has something else in store and it's bound to be good. Yes Luffy may not seem like he's ready for all sorts of further opponents after this. However the Rayleigh flashback hints to something else Luffy might have in store for the future, and I like that. Luffy didn't just pull gear four out of thin air and then another mode maybe out of thin air too. Luffy had a legit reason to ccome up with something new and it was thought of in the time skip.
–- Update From New Post Merge ---
@Omni:
So here is what I think should be gleaned from the conversation with Rayleigh
Gear 5th Hint seems obvious.
There were monsters on the island that Kong punch didn't work on… I gurantee we'll see the former boss of the island before Luffy took over and that's where we'll see him quote "Beasts that won't be tamed need put down" It's incredible to think there were monsters strong enough that Kong punch didn't work on them, yet it worked on Doflamingo resisting.
I think there were beasts there with tougher armour and bigger. But Luffy just created a bigger Kong Gun. The king.
Rayleigh did state there were 500 or so beasts stronger than him at the start