It has never been established anywhere, saying something repeatedly doesn't make it true
The only thing we're told is that Sanji's blue flames > Sanji's fodder tier orange flames

The only thing we're told is that Sanji's blue flames > Sanji's fodder tier orange flames

Falme temperature is directly correlated to temperature. I used google search as a souce. You can chose to be asshole and think you know better.
Red:
Indicates the coolest temperatures, often around 500°C to 800°C.
Orange:
Represents a slightly hotter temperature, generally between 900°C to 1,100°C.
Yellow:
Signifies a further increase in temperature, with flames typically ranging from 1,200°C to 1,300°C.
Blue:
A blue flame indicates a very hot flame with temperatures potentially reaching 1,400°C or higher, particularly when the combustion is complete.
White:
The hottest flames, usually bluish-white, occur when temperatures exceed 2,700°F (1,500°C).
Ace is generally at Orange range.
Magma also has temperature range typically 700°C-1300°C. Some types of magma goes up to 1600°, but I don't know if Akainu's magma is of that type. Hard to quantify where Akainu's temperature will be by this data, but Akainu says his magma is hotter than Ace's fire, so that would put him around 1300°C.
Sanji's flames are blue, so he around 1400°C mark.
Sanji's flames beat Akainu's in theory, but Oda can chose to give Akainu higher temperature by modifying his Magma type.
The destructive power of Sanji is always downplayed, but Sanji can cook your insides easily with Ifrit. Able to hurt Luffy in G5 is not an easy feat.