I managed to answer this, hope serves someone if interested. The answer is not straightforward but rather gives an inferior limit to it. According to
this post, the RIVE with at least BIOS 3404 (but earlier BIOSes could also support this) does seem to support UEFI specification 2.3.1 (with at least errata B revision). This is because Windows 8/8.1
requires this same specification to run secure boot.
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Rampage IV Extreme BIOS 4206
Intel I7-3820
32 GB Quad Channel Kingston Hyper X Genesis
2 x Nvidia GTX 690
2 x WD Velociraptor 250 GB RAID0
Intel 120GB 320 SSD
Noctua NH-D14 SE2011
CM Silent Pro Hybrid - 1300W
CM HAFx