Performance testing aims to ensure the operational efficiency of software systems. However, many factors influencing the efficacy and adoption of performance tests in practice are not yet fully understood. For instance, while code coverage is widely regarded as a key quality metric for evaluating the efficacy of functional testing suites, there is limited knowledge about the types and levels of coverage that performance tests specifically achieve. Another important factor, often perceived as a barrier to the broader adoption of performance tests yet remaining relatively unexplored, is their extended execution time. In this paper, we analyze the performance testing suites of 28 open-source systems to study (i) the magnitude of their code coverage, and (ii) their execution time. Our analysis shows that performance tests achieve significantly lower code coverage than functional tests, as expected, and it highlights a significant trade-off between coverage and execution time. Our results also suggest, in perspective, that automated test generation methods might not ensure affordable performance testing due to the associated time cost. This finding poses new challenges in the field of performance test generation.