Mass FPS lag in Tekkit server

[Xephex]

I am running a private tekkit server with around 5 of my freinds. Even when I am alone online In certain chunks I get 1FPS and so does everyone else when I leave these chunks my frame rate jumps back up to around 200. This cant be a problem with my PC as its a i7 3770k 6GB ram and nvidea GTX 560.

Please help The server is unusable I have installed Anti-lag mods and there is no change. I rarely use build craft pipes so it isnt the entities.

PLEASE HELP!

Thanks for your help

Morgan