Ifrit Jambe must be stronger than anything with Adv.CoA, so Sanji already surpassed this level in this chapter
Like Marco's attacks, Queen mentioned shockwaves, they looked much better against King than anything Zoro has used, including ShiShi Son Son (one of his strongest moves). Both King and Queen tanked these blows pretty well.
So it means that for you to beat King and Queen, you need to start with Adv.CoA and then progress to something considerably stronger
Just a matter of time for Queen to say how much Ifrit Leg is hurting his whole body, like Jabra did to Devil Leg, much more than Marco's attacks with shockwaves.
I have a headcanon that Sanji and Queen's final clash will end with Sanji bypassing Queen's haki, so Queen complains that even his haki can't handle Ifrit Leg anymore.