The best known asymptotic bit complexity bound for factoring univariate polynomials over finite fields grows with the input degree to a power close to 1.5, and with the square of the bitsize of the ground field. It relies on a variant of the Cantor-Zassenhaus algorithm which exploits fast modular composition. Using techniques by Kaltofen and Shoup, we prove a refinement of this bound when the finite field has a large extension degree over its prime field. We also present fast practical algorithms for the case when the extension degree is smooth.