A process that makes an important difference between $C_3$ and $C_4$ plants is:

Photorespiration occurs in $C_3$ plants when RuBisCO binds to oxygen instead of $C{O}_2$. $C_4$ plants have evolved a mechanism (Kranz anatomy and the PEP carboxylase pathway) to increase the concentration of $C{O}_2$ around RuBisCO, thereby virtually eliminating photorespiration. This makes $C_4$ plants more efficient in high temperatures.