No, it's not the PCI connector, I know what those ones are (kind of sort of; they have big labels on them so they're hard to miss lol)... this actually says, on both the power supply, the cable, and the motherboard, "CPU 8 pin". And there was a sticker on the motherboard (otherwise I wouldn't have noticed) which said "supports extra CPU 8 pin".
It's the Gigabit GA-X58A-UD9 R, and I'll be running an i7 980X, so it needs all the juice it can get
The motherboard manual says that extreme editions need to run with the 8 pin for stability purposes.
EDIT--D'oh! I went in and looked more closely at the manual, and it does say to use a 2x4 for the cpu... so what was the 8 pin CPU cable that was connected to my power supply, and why is there an extra 8 pin connector on my motherboard?