First of all:
"Don't ever use the 5930K unless you're using a Quad-GPU setup. The 5820K is pretty much the same, just without the Quad-GPU functionality. "
100% incorrect.
Not to be rude, but when someone comes and asks for advice, know your stuff before you respond please.
Every card uses bandwidth.
A 4x slot will draw 4 lanes.
So if you have a thunderbolt, 4 lanes are used.
If you have a thunderbolt and a wireless card in 4x each, 8 lanes get used(uncommon config).
If you have a thunderbolt and a 1x wireless 5 lanes get used(Very common for X99 based systems)
A single graphics card will, on most x99 boards, draw 16x, and almost every x99 bios with the exception of the ASROCK EXTREME Line I believe it was, will not allow you to choose 8x if you have one graphics card installed.
Additionally, Most boards, do not allow you to have two cards in 8x.
For example, the Sabertooth X99, one of the most stable X99 Boards, requires the master card be in 16x.
So lets say for example, you have One 16x Graphics card, a thunderbolt and a wireless card (21 lanes, and a 5820k, You cannot install another graphics card, as neither AMD nor Nvidia Support 4x SLI on the X99 Platform. (Nor do they support 4x non-SLI)
So if you want 2 graphics cards and 5 more lanes for peripherals, you WILL need a 5930k.
I hope this helped you on the GPU's Portion. BTW, the best GPU money can buy right now is the ASUS Strix OC 980ti. Blows everything else out of the water.
Cheers