Version 5.01 specifically focused on bug fixes, performance improvements, and better handling of multi-core processors. It represents a "golden build" — stable, fast, and free from the telemetry or cloud-integration features found in later versions.
WinRAR 5.01 takes full advantage of multi-threading. On a 64-bit system with a quad-core CPU, you will see compression speeds nearly 2-3x faster than version 4.x. WinRAR 5.01 -32bit - 64bit -full version