You may experience low FPS (frames per second) in your lovely game modifiaction Tekkit for Minecraft. It is because the Minecraft itself is not fully optimized as it is written in Java.
Minecraft also have some stuttering issues in big cities on high-end computers with plenty of cores and RAM. What we can do?
The only solution is tweaking and modding. If you are experienced user, then you will have no problems and can download mods and patches, but many users will. So we have developed automatic installer named Tekkit Tweaker, which will allow you to install modifications, optimize your configs and more.
For older computers we recommend lowering render distance and Fast option in Quality settings.