The relationship between latent trait and test-taking speed is an important area of study in assessment research. In addition to contributions of such studies to psychometrics, the factors that affect both ability and speed have implications for test development and have policy consequences especially if the tests are high stakes. This study investigated the main assessment scale used in gifted education screening in the Kingdom of Saudi Arabia and focused on the discriminating properties of items across the several cognitive subskills being measured. Under an item response theoretic framework, this study used a lognormal response time model to investigate the discrimination parameter estimates for both ability and speed, with guessing taken into account. Results showed that cognitive subskills do not have uniform discrimination properties across ability and speed, such that some types of items are better at discriminating ability while other types are better at discriminating speed. At a test-level, our results also showed that ability is negatively correlated with speed, such that higher ability students tend to take more time and hence have slower speed. This finding supports other results in the literature. Implications for high-stakes testing and test development are discussed.