Major FPS Drop with smooth lighting

In general, a have a massive FPS drop from 1.4.7. If I stay idle for a bit with smooth lighting on minimal, the game will run decently at 30-50, but if I start to look around fast with only sensitivity at 100%, my fps decreases to 15-25. It seems turning smooth lighting all the way off will increase performance to what it was on 1.4.7