Docker containerization has been extensively studied over the past decade, and a general consensus has formed around its performance characteristics. Studies running on native Linux platforms — Felter et al. [1], Potdar et al. [4], Mavridis and Karatza [5] — consistently report less than 5 to 6 percent execution overhead and 20 to 30 percent memory efficiency gains. More recently, a small number of studies have begun examining Docker on non-Linux platforms. Sladovic et al. [9] tested Docker across Windows, macOS, and Ubuntu in 2024 using compilation benchmarks and found Windows with WSL2 retained about 94 percent of native Linux performance. Sergeev et al. [11] compared Docker on Windows and Linux in 2022 and found only marginal arithmetic and memory performance differences between the two platforms. However, these cross-platform studies share a limitation: they used general-purpose or compilation benchmarks rather than high-concurrency web application workloads. The performance of Docker on Windows WSL2 under concurrent HTTP request loads — the scenario most relevant to web application developers — has not been systematically measured. This paper fills that gap by running four controlled experiments on a Windows 11 machine with an Intel i5-12500H Alder Lake processor under sustained concurrent workloads: application startup time, concurrency scaling from 10 to 200 users, memory consumption across workload sizes, and sustained execution under peak load. Our results reveal a more significant performance gap than prior cross-platform studies found. Under high-concurrency compute-intensive web workloads, Docker-on-WSL2 showed 58.1% execution overhead — far higher than Sladovic et al.\\\'s 6% and Sergeev et al.\\\'s marginal difference. We attribute this to the WSL2 virtual Ethernet bridge, which adds consistent per-request overhead under concurrent load that compilation benchmarks do not exercise. Memory efficiency of 25.3% reduction was confirmed consistent with prior literature. Additionally, Docker achieved near-complete CPU saturation of all 16 Alder Lake threads through the Linux CFS scheduler — a workload-dependent advantage that prior cross-platform studies did not document.