Usually, the overclock by the manufacturer is where the card is most stable at. If you plan on overclocking get the cheaper card. If you want to save yourself from doing any of that the Gigabyte OC will be good for you. And the cooler on the card is much better than the original (reference) version. It's useful for getting higher clocks, because heat usually goes up.
Only get non-reference cards with coolers like the Gigabyte if your case has a very good airflow. Those type of coolers dump a lot of hot air into the case usually making the upper card run hotter, and sometimes overheating it. That being said, you probably wouldn't see that big of an overclock on the reference cards, but at least they won't drown each others in hot air.