@Maarten Thijs
This was always an issue with smooth lighting. I doubt most people who used to play max setting do not want to turn down to "fast lighting" in order to get their regular FPS.
B version of snapshot helped a little. The FPS is very rough though if vsync is disabled. For example, I get 120 FPS (or so the game says), but it feels like ~30-40.
So Jeb just tweeted that most of the FPS drop may be due to this bug fix: https://mojang.atlassian.net/browse/MC-997 (Source: Jeb's Twitter)