i7-6700k is fantastic for gaming and Twitch streaming; higher base clock
i7-5820k is very good for gaming and great for content creation; more CPU cores (6 versus 4 for the 6700k).
* I chose the 5820k because it has 28 PCIe lanes versus the 20 PCIe lanes for the 6700K. If you only plan to upgrade your GPU's to 2 way SLI, then either CPU is fine. But if you plan on adding more PCIe devices, such as NVMe SSD's, then it becomes an issue. Eventually I plan on upgrading to a 40 PCIe lane CPU, for when I go 4 way SLI.