We study a three-wave truncation of the high-order nonlinear Schr\"odinger
equation for deepwater waves (HONLS, also named Dysthe equation). We validate
our approach by comparing it to numerical simulation, distinguish the impact of
the different fourth-order terms and classify the solutions according to their
topology. This allows us to properly define the temporary spectral upshift
occurring in the nonlinear stage of Benjamin-Feir instability and provides a
tool for studying further generalizations of this model