In my world I have a contraption called "Iron Foundry" created by TangoTek. In newest snapshot if I'm near by (or all the chunks containing contraption will load) game starts to shoot at me with literally seconds of delay all the time. However, in console there's no sign of this delay - there's no thing like "Can't keep up! Did the system time change, or is the server overloaded? Running xxms behind, skipping xx tick(s)" and game runs smoothly with max FPS. Just all entities and redstone mechanisms lag.
I don't have powerful PC, but if it runs on max FPS that means there's no strain on CPU I guess.
I'm attaching his world download for you to check it out for yourself if you experience the same.
EDIT: Doors are causing this lag. I've been removing them by hand one by one and while I was cleaning up more and more the game started to keep up and finally everything went back to normal when I've destroyed all of them. These doors are converted to 48 villages I believe. So the cause of this delay are doors or villages.