The game lags down to 2 fps when the player looks at a cluster of command blocks. Otherwise 30+fps is the average. Only in 14w04a.

See this bug in action: http://youtu.be/nsUtoAhviyM The command blocks all have testfor, fill, clone and blockdata commands in them, if that's relevant.

I looked at other tickets before making this one, all the others seem to be affected by other versions, unlike this one.