Superclocked does mean it comes pre overclocked. If the stock clock for the 760 is 980MHz, then a 1GHz 760 could be "superclocked".
ACX is a cooler design, probably. Some companies design a cooler and slap it on all their cards. For example, I have the "wind force 3" cooler on my Gigabyte card. Gigabyte designed a cooler that has 3 fans and called it that. Then they put it on 7950s, 7970s, GTX670, etc. It's often called the WF3. Another company made a cooler they call "Double D". ACX is just another non stock/reference cooler. I'm not sure of which cooler that is however. Or how it compares to other coolers. eVGA is a good company however so I would buy a card from them.