I am unsure if this is a duplicate, While playing minecraft there sometimes are random lag spikes, My setting are like they were in 1.5, graphics fast, smooth lighting Medium, ect. I am not the only one that has experienced this as many others have said so (forums), some have said it is the way the graphics are rendered, and some have said it increased there fps. not sure if this is spam, but this is where I got my information http://www.minecraftforum.net/topic/1798520-13w18c-unbearable-lag/ thankfully I do not drop to 10fps, I would get around 37fps at most and then have it drop to 15fps at minimum and steadily gain back up again, then falls back down while loading chunks.

while looking in the dev launcher console I see/seen SERVER WARNING Can't keep up! Did the system time change, or is the server overloaded? and the time never changed, last time I played I got this spammed a lot, unfortunately I could not find that log.