3,000 Degrees Celsius
The Movie: Tony Stark figures out the larger Mandarin/Killian puzzle by investigating explosions with a heat signature of 3,000 degrees Celsius (around 5,500 degrees Fahrenheit). Turns out, the Extremis hit men can approach this temperature, easy peasy.
Real Life: We give the movie points for using the Metric system instead of the dreaded Imperial. However, are we really supposed to believe that these Extremis weirdoes reach temperatures much hotter than lava without having any effect on their environment? Have you ever seen molten rock wearing clothes, for example? Could a magma-man hang out on a plane without burning through the floor? Or trade insults with Tony Stark without melting his face off? If you have ever felt sunshine, you can attest to the fact that heat is diffusive — it doesn't just stay bound to the object producing it. We love you Guy Pearce, but please leave Burning Man to the hippies.