The options are for two 8-pin connectors. The board will run with just one 8-pin connector plugged in for CPU power. Make sure you plug it in the correct 8-pin connector (not an issue if both 8-pin connectors are plugged in).
You are right about the 2nd 8-pin connector needed only for extreme OC.
What type of PSU do you have? On my EVGA board I obtained a second 8-pin connector and plugged both 8-pin connectors into the motherboard sockets. You will need something like this - http://www.microcenter.com/single_product_results.phtml?product_id=0318698
Power cables for PCI are different from power cables for the motherboard (read it on Corsair's website)