Zotac use reference PCB, EVGA use PCB that include higher power target circuity, in simple term higher delivery allow GPU to operate at higher clock = more FPS, faster rendering, and more efficient on watt consumption.
With ~US$100 more, you can get Asus 1080 Turbo or MSI 1080 Armor (non OC version), is it worth for SC, yes, it's one of the best GTX 1070.