My friend is also experiencing the extreme lag on his high end rig, when it was almost non present for both of us on 1.7.10. But my system specs are AMD Athlon X4 760K quad core 3.80 GHZ processor, 8 GB of Ram, the game is run on a 500 GB Samsung SSD, and I have a Radeon R9 270 Graphics card. My graphics are on fancy, render distance is 12 chunks, clouds are fancy, particles are on all, VSYNC, VBO, and shadows are on, Smooth lighting is at Max, and max frame rate is set to unlimited.