Bump....
Same issue here its gotten worse. Ive basically reinstalled Windows 8.1, drivers, updates, and precision X 16 5.3.1. Right after I log in my keyboard input is extremely slow for ~15 seconds there is a huge typing lag (as soon as I log in I open notepad, npad++, or firefox and can clearly see typing lag as I mash keys). All the keys I pressed will eventually catch up all at once after ~15 secounds. This only happens with PrecisionX enabled (either just startup settings or starting the whole app with windows).
System
5930K
Rampage V Extreme
Corsair Dom Plat 3200 16GB RAM
EVGA 780GTX Classified HC
Corsair K70 RGB
Logitech G13
No other monitoring software or any software except for Windows 8.1, Drivers, and all OS updates.
Now this issue appears in older versions but lasts only 2 seconds or so (like 5.2.5 and 5.2.7). Uninstalling PrecisionX 16 will remove this issue. I have also tried 2 other keyboards and uninstalled the corsair/logitech software with no change with the above behavior. Of the few previous versions I can find it seemed like 5.2.7 was the best. I also tried that other popular GPU overclocking software which works with no issues as well but I'd rather not use that software unless I have to.