I couldn't tell you why, however doing a clean reformat with the K70 RGB plugged in (single USB 3) caused continuous hangs and errors during the installation process. I'm onto my second Windows 8.1 installation, after having tried installing Win7 twice beforehand with the K70 equipped.
OS were loaded on different USB drives during the process, to remove that as a factor. SSD being installed to is less than a month old, too, and hasn't given me any issues before CUE and the K70 RGB.
Coincidentally, I'm also running an ASUS motherboard:
CPU: Intel i5 4670k
Mobo: ASUS Z87-C
RAM: Corsair Dominator Platinum 16gb (1866)
GPU: Gigabyte G1 GTX 970
SSD: Samsung 850 EVO (500g)
HDD: WD Black 1TB (unplugged during OS install)
HDD: WD Green 3TB (unplugged during OS install)
PSU: Corsair HX650