Lag Spikes / FPS Drops

Ever since I updated to the Snapshot 13w04a(also 13w03a), I've had massive FPS Drops in the Overworld, which has made me pretty much unable to play. This doesn't affect any other dimension, as I have about 96-160 FPS over all in the end, and 110-180 in the nether. Back in the later snapshot (13w02b) I never had this problem. But now I can't get more than 16FPS in the overworld.