Alright.
So right off the bat, we see Base X-Drake
react to and dodge attacks from Apoo. Apoo was the same person who could
dodge Zoro's hits. Zoro was able to content and was relative in speed with Flame on Base and Zoan forms King.
Pre-Awakening Base Sanji, was only
able to react to
Zoan X-Drake, but he scales relative in speed to Hybrid Queen who should be at least to his Human form, which was able to
tag and put X-Drake down.
All of this proves that Post-Awakening Sanji already scales above Flame On Base and Zoan King.
Now, for Flame Off King, it gets a little bit trickier. We already know that Pre-Awakening Base Sanji scales above Flame Off King in speed and we already know Post-Awakening Base Sanji is faster than Pre-Awakening Base Sanji due to the fact that after his awakening, his Diable Jambe was shown to be faster than it was before then, so the same should apply to his base.
Flame On Base King < Flame On Zoan forms King < Pre-Awakening Base Sanji > Post-Awakening Base Sanji
Flame Off King scales FTE to his Flame On form. Although this is impressive, Post-Awakening Sanji has amps that make him many FTEs above his already superior speed to Flame On King
Flame On Zoan Forms King (FTE)< Flame Off Base King < Flame Off Zoan Forms King
Post-Awakening Sanji's FTE's are the following: Enhanced Speed, Diable Jambe, and Ifrit Jambe. Sanji has shown that he can stack his Enhanced Speed with any of these forms.
Post-Awakening Sanji (FTE)< Enhanced Speed
Post-Awakening Sanji (FTE)< Diable Jambe
Post-Awakening Sanji (FTE<)< Ifrit Jambe
Post-Awakening Sanji (FTE + FTE)< Enhanced Speed + Diable Jambe
Post-Awakening Sanji (FTE< + FTE)< Enhanced Speed Ifrit Jambe
And although this is enough to prove that Sanji's top speed is superior to King's Flame Off speed, that is not it for him. King also has Imperial Deep Pride Stake, which blitzed Zoro, who scales to Flame Off
Flame Off Zoan Forms King (FTE)< Imperial Deep Pride Stake.
Sanji scales much higher in speed.