Ah dam, you can install them in any PCI-E slot, 16x slots are backwards compatable with 1x, 4x & 8x devices
Also it doesn't slow any of the other slots, my GFX cards still show 16x
The only disadvantage I have found is the need for a floppy power connector - more cables lol

On my Rig 3 I use an Adaptec PCI-E RAID card in a 16x slot, and I havn't noticed any overclocking issues with it either.

Sorry mate, wish I had been able to tell u pre order