same issues here.
just un-installed newest and re-installed the 3.18.77 from a link on previous page and all is good again.
i noticed the crazy system slowdowns mainly when i was downloading fast/large files, or even running a speed test. this really made no sense to me since it was internet/network usage. however, anytime my net usage was high, the mouse started becoming unresponsive for several seconds over and over.
went through a lot of wasted time messing with NIC drivers, video card drivers, etc, and in the end it was iCue.
after i saw this thread, uninstalled iCue, rebooted to no iCue installed, all was fine. installed 3.18.77, all is good.