I'm unable to boot at all here Miahallen, 777 or 888, high voltages don't help either (ES D2)

I'm using Mushkin MGH's, and these can do 777-21 @ 2000Mhz triple on X58 with only 1.72, haven't tested to see what they can do at 2133.

It does look to me like either BIOS slight incompatibility, or an IMC per CPU issue since it works at lower CPU freq for some. I haven't tested that myself, I was only trying at 5Ghz I think.

Was testing using F7a, will try again later with F7d at stock CPU speed and 5Ghz

Your above testing is on Asus, can you do the same on GBT?