edited: original post edited to better reflect results of testing.
vsync off: graphical tearing, but best performance.
vsync on: timed stutter every 4.5 seconds (or slightly less than 5 second intervals). sometimes 1+ seconds? inconsistent.
adaptive vsync: still exhibits tearing, although to a lesser extent than vsync off. also causes graphical tearing/artifacts related to UI and HDR bloom. lower performance. sometimes panning seems laggy.
top/left mouse input: moving the mouse slowly towards the upper/left direction fails to produce camera movement (at 4000 dpi, problem is worst, even at 200 dpi there is a noticeable 30% difference in lack of top/left input). other directions unaffected. (while rotating the camera)
logitech g400s, sapphire radeon hd 7850 ghz ed, catalyst 14.12
further comments might add some description to the problem, as it’s been revised.