Hummingbirds are capable of flight over a wide range of flight speeds, from hovering to rapid forward flight. The load lifting assay tests the maximum amount of weight a bird can lift. This assay has been widely used because it requires simple, field-portable equipment. However, it represents flight performance at low flight speeds. Here we ask: is performance of low-speed and high-speed flight correlated? We tested this by flying 50 wild hummingbirds of four species (Calypte anna, Calypte costae, Selasphorus sasin, and Archilochus alexandrei) in the load-lifting assay as well as measuring their top speed in a wind tunnel. As these species are all sexually dimorphic, and the species also vary in body size and wing loading, we used path analysis to ask: what determines the maximum forward flight speed of a bird? The best-supported path model suggested wing length and keel size (a proxy for flight muscle mass) best predicts load lifting performance, while wingtip velocity (proportional to wing length multiplied by stroke amplitude and wingbeat frequency) and keel size predicts top speed. However, load lifting ability and top speed are not correlated and do not covary, despite both being partially predicted by keel size. These results suggest lifting extra mass vertically and fast forward flight are limited by different morphological traits and are fundamentally different processes.