At MySQL, we know our users want Performance, Scalability, Reliability, and Availability, regardless of the platform the choose to deploy. We have always had excellent benchmarks on Linux, and with MySQL 5.5, we are also working hard on improving performance on Windows.
The original patch of improving Windows performance was developed by MySQL senior developer Vladislav Vaintroub; benchmarks by QA engineer Jonathan Miller. We integrated the patch into MySQL 5.5 release.
The following two charts show the comparison of MySQL 5.5 vs. MySQL 5.1 (plugin) vs. MySQL 5.1 (builtin) using sysbench: