When running Minecraft 1.7-1.7.9 I get around 100 fps on fancy graphics, minimum smooth lighting, 12 chunks, and my memory usage stays steady. When I load up any of the 1.8 snapshot versions, I get around 20-30 fps on the same exact settings except my memory usage rapidly changes from 40% to 50% so fast that you can only see the 4 and the 5 when it alternates.