the i7 5820k will run SLI fine. it has 28 PCIE bus. which means runs 1 card brilliantly and will SLI 2 cards.
Its only going to be 3 or 4 card SLI when you want to go to 5960k for its 40 PCIE bus.
So unless your looking TRI SLI or QUAD SLI its good for the cash