Massive lag spikes - even with low video settings

In 1.5.2 - with high video settings (such as: fancy graphics, far render distance, bobbing on) frame rate was around 36fps
In 12w22a, I'm experiencing large lag spikes. I've turned graphics to fast,render distance to tiny and bobbing off. Sometimes it's 36, but lag spikes happen every 5 or so seconds.
I've turned off the beacons in the near vicinity just in case it was that. No, it wasn't, still getting frequent lag spikes