Low FPS when loading chunks, same on far as on tiny ~30-40 FPS, game overall choppy

BIG FPS drop when chunks are loading, normaly running at 160 FPS on far and ~400 on tiny. Whenever I move so chunks start loading (even if I have played for an hour or so) FPS drops down to ~30-40 on both far and tiny and everything becomes very strange and choppy. Everything ran fine on 1.4.7 at a constant rate of about 160 FPS. Image taken at render tiny, no difference whether I use smoothlighting: minimum or maximum. Smoothlighting: none restores the framerates to what I had in 1.4.7 but makes everything look as it does with it turned of. Thinking my computer should be able to handle it better than this...