Not gonna lie but that speed feat is indeed impressive. Even if we consider it's a short time burst like a blitz even then having such speed is hell impressive.
Oda literally drew the panel highlighting his disappearance as if he went invisible.
This is the best PU he has received.
As far as his hot flames is concerned then I am a bit off regarding it.
It seems Sanji used hardening and exoskeleton to protect his leg from hotter flames.
So, this means if anyone has better CoA then his hotter flames might not do much damage.