Ecologists have traditionally used maximum performance as an indicator of the likelihood of task success. However, this is not always the case: individuals do not necessarily need to be able to outrun a predator using their maximum speed, and may instead employ tight turns to outmanoeuvre it and escape. The functional performance trade-off between speed and manoeuvrability means that the faster an individual runs, the less manoeuvrable it becomes. Selecting the optimum running speed becomes a matter of finding the perfect balance between these two performance traits for a given situation. We would expect animals to evolve toward their optimum performance in tasks where the stakes are high. However, whether individuals choose to perform at this optimum in different ecological settings is likely to be dependent on a variety of physiological and environmental factors. Our work uses optimality modelling to predict the optimum running speed when there is a trade-off with manoeuvrability in a native insectivorous marsupial, the buff-footed Antechinus (Antechinus mysticus). We then use experimental tests to determine whether Antechinus choose to employ this optimum speed in different ecological settings, where they act as either a predator or a prey species. These kinds of trade-offs offer explanations as to why seemingly unintuitive behaviours are exhibited in the natural world.