Parallel streams in Java 8 offer notable performance enhancements for both IO-intensive and CPU-intensive tasks compared to single-threaded solutions, providing up to 7.25 times faster execution for IO tasks and 4.2 times for CPU tasks. This performance boost, however, requires careful configuration of thread pool sizes to prevent overhead and performance degradation. A series of tests comparing ExecutorService, Fork/Join Framework, and Parallel Streams revealed that while parallel streams deliver superior results for large-scale IO tasks, they can also underperform if not properly configured, especially on machines running other multithreaded applications. The tests emphasized that while parallel streams generally handle thread overloads better, selecting the appropriate method depends on the specific task and system configuration. For CPU-intensive tasks, all implementations showed similar best results, with parallel streams being consistently reliable across different thread counts. The study underscores the importance of understanding hardware capabilities and the total number of threads in an application when applying parallelism, suggesting that similar tests should be conducted in a staging environment to optimize performance outcomes.