if you own 5390K the upgrade would be minor
if you upgrading go for more cores at least,
also PCI-E lanes are not important
7700K with only 16 lanes handling 2 1080Ti's easily
I've got the 6800k in the machine at the minute running at 4.25ghz 1.3v runs smooth and low temps. My 5930k was from my old titan X sli build. Just wondering whether to keep or sell.