are you using the PCIE 3.0 8x8x slots are you using the x16/x4 slots.
x16/x4 is not enough bandwidth for xDMA bridgeless crossfire. I had similar issues until I changed to 8x8x
Interesting. I'm not sure that furmark uses multiple GPU's properly, I haven't looked into it though. Make sure you disable V-Sync in the CCC, although some games (especially particularly broken ones like Far Cry 4) will have FPS limited to 60 even when V-Sync is off ingame and in the CCC. Go figure.
Haha! That's all it was... Jeebus chrust! Literally. An entire week of trying to get crossfire to frickin' work, and all I actually needed to do was update my bios. Rip gaben. Rip me. Rip all that is luv. Rip all that is LYF. Thank you guys for your help! Honestly.