Downloads approaching 0x7FFFFFC7 bytes slow to a crawl
Basic fix should be a one-liner.
More interesting optimizations include dropping StreamAndForget to ~262mb for all users (not just 32bit) and replace MemoryStream in PipeReadBuffer with a RecyclableMemoryStream or similar data structure.
Fuller explanation: https://textslashplain.com/2017/07/09/working-with-big-data-in-net/