The maximum theoretical efficiency $\eta$ of a heat engine is given by the Carnot efficiency formula $\eta = 1 - \frac{T_C}{T_H}$, where $T_C$ is the cold reservoir temperature and $T_H$ is the hot reservoir temperature (both in Kelvin). If a steam engine operates with a hot reservoir at $327^{\circ}\text{C}$ and a cold reservoir at $27^{\circ}\text{C}$, what is its maximum theoretical efficiency? (Note: $T(\text{K}) = T(^{\circ}\text{C}) + 273$)