If you haven't bought any of this I'd possibly urge a build rethink. I'm assuming you are getting an 850W PSU to cover yourself for SLIing GTX780Tis, but there's much better PSUs to buy than the RM850. The Hero is pretty expensive too, relative to what it brings to the table.
To answer your actual question, the Maximus VII Hero uses an 8pin EPS connector and a 24pin power connector.
Just using overclockers and black coloured Bitfenix extensions as examples (obviously you can change these)-
24pin
8pin EPS
Not all GTX780Tis are identical, some will have two 8pin power connectors, but the standard reference configuration is for one 8pin and one 6pin PCIe power connector.
8pin
6pin
If you know which card you are getting already, it's pretty easy to figure out, but if you aren't 100% sure, you can always get a
6+2 PCIe lead which can serve as an 8pin or as a 6pin with the extra 2pins dangling. It's not super tidy though, and if you are buying expensive extensions it seems like a waste.