Replay Speed Unlocker library (module) is dedicated to remove x8 replay speed limit in Warcraft 3.
1.24e/1.26a/1.27a/1.27b/1.28f
Simple place this file in your Warcraft III root folder or in Redist\Miles that also resides in the root folder.
This probably won't work in Multiplayer Replay Viewer, as it was not tested.