BIOS 1604 runs pretty decent here on M V Extreme with UEFI boot to Windows 8 x64, actually it runs better than I expected, amazingly some of nvidia driver issues disappeared in UEFI boot mode...
whoever told you that updating/flashing motherboard BIOS voids warranty fed you with the biggest lie I ever heard ... even Asus technical support may ask you to flash to this version or that in order to fix some problem, same goes for their beta BIOSes (some not even published yet).
.: R3C0NF1GUR3D :.ASUS MVE :: 3770K bench @ 5.2GHz (delidded) :: 2x4GB Mushkin 996990 @ 2400MHz CL10 @ 1.7V :: evga 670 2GB SLI @ 1280/7108 :: Mushkin Chronos 240GB SSD RAID0 (OS) :: WD RE4 2TB (storage) 2TB :: Hitachi Deskstar 5K300 2TB (backup USB3.0) :: ASUS VG248QE 24'' 144Hz monitor
My rig with pictures"We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle