I'm experiencing this exact issue as well, just like rikailp describes. It occurred on the transition from Mindcrack v7 to v8.01 and is not improved by adding or removing Optifine. My framerate also dropped from ~75 to ~30 in my main base. The rendering/fps issue doesn't seem as bad away from my processing equipment. More on the lines of fps issues, I took a few screenshots. Here is what I experience in my base now, with v8.0.1. This is with all the same settings, moving about 180 blocks outside of my base. And this is in that same spot with my settings turned down.