IMPORTANT: THIS REQUIRES AT LEAST FORGE 18.104.22.1689
Update to Minecraft 1.12, includes too many bugfixes to list all of them. Marked as Beta due to the unstable Forge releases, as well as the potential for bugs due to the under the hood changes.
The biggest change is that the render code has been rewritten, and the networking code as well. Networking is now managed by Concrete, and the rendering code now uses VBOs or display lists depending on your settings. You should notice a general increase in performance on larger creations.
NOTE: This is a reupload, the previous version was missing Concrete for networking.