How can I determine why keyboard response is intermittently very slow with large display? I'm using a Seiki 4k display model SE39UY04 connected via HDMI with a Retina, 15-inch, Early 2013 MacBook Pro at 3840x2160 @ 30 Hz running Mavericks.  I've noticed that with the laptop closed and only displaying on the external display, I sometimes find in Chrome that bluetooth attached keyboard response is very sluggish.  For example, I can type a sentence on a web page but nothing appears at first, then a few words, and finally the rest appears quickly, however, the delay between typing and completion of it showing up can be 30 seconds or so.  I've looked at the Activity Monitor and do not see any CPU hog, the machine is relatively idle and the fan is not running on the laptop.

How can I figure out the cause of this intermittent delay that seems to have appeared with the introduction of the very large external display?
This is a bug in Chrome as recorded at google as issue 319580.

The other symptoms as described in that bug report are that display update is very slow when the animated icon for the browser tab is on any 4K display such as the Seiki 39 mentioned in the question.  One work around is to move the browser tab animation off screen and performance returns to normal.  There is a fix forthcoming to Chrome that is available now in the Canary builds.