Post a screenshot with F3 enabled and your JVM arguments.
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Say something silly, Laugh 'til it hurts, Take a risk, Sing out loud, Rock the boat, Shake things up, Flirt with disaster, Buy something frivolous, Color outside the lines, Cause a scene, Order dessert, Make waves, Get carried away, Have a great day!
You may want to try reducing the "biome blend" option in your video settings. A few friends and I were trying out the new update earlier today, and one of my friends' PCs would dip from 500+ FPS to near 0 whenever multiple blocks were placed/broken near him. Supposedly, he had that biome blend setting set to 11x11. Setting it to 5x5 (or lower) fixed the problem for him.