Severe FPS spikes/drops when Advanced OpenGL is set to on and weird world generation lighting issues

There wasn't an option for both so I just said none for game mode. The issue is though, that while playing there will be seemingly random FPS drops. It's weird because in 1.5.2 I usually maintain about 20-25 FPS and in this version I'm usually at around 25-30. When Advanced OpenGL is on though there will be random drops to 0 or 1 FPS which I thought practically impossible.