Iv'e come across a bug in this latest snapshot. I took the time to test this and seems that redstone moving between chunks that are loaded and unloaded causes severe lag across the server to ANYONE whos WITHIN the area of the user causing the lag. The pictures below show a Mob farm i setup in a Server running 13w39b. When moving away from the mob farm, once the redstone becomes half loaded and any tick update happens frame rates just drop drastically to the point you cannot move or talk as the 3rd last photo shows.

Also as you can see in MCedit the redstone crosses over a 4 chunk intersection in one point.

Iv'e also uploaded the world so anyone can test my theory. Here is the link (The file is Zipped)
https://www.dropbox.com/s/or8kgff3so6hjq4/The%20Devils%20Kin.rar