My computer works really well with minecraft. At 8 chunks I can get reach 200 fps. After updating to 14w04a, I logged into my friends multiplayer server (same issue in SP) and was struck by the amount of lag i would get. I would drop deep into the 20 fps range. When standing still I found my computer going up in fps. It seems to occur when more chunks get loaded. The chunk updates are usually around 300-400 when moving. Sometimes I can hit 1000

The first picture is when I am in motion. The second is my video settings. And the third being when i stand still