Its a Hiper 530w.
Depends on the rest of your system. It should be enough but you won't have much overhead as the +12v line is only 360W. Considering it's efficiency, wattage and your planned use I'd think about replacing it once you have the funds.
Also, after my experience with a BFG factory overclocked card, and what I've seen from some threads here plus some etail user reviews I am wondering if the overclocked cards have had a BIOS update that upped their voltage? Has there been an issue here?
I believe there were no bios updates and I wouldn't hold my breath. Overclockability depends on each GPU and some will work with factory voltage while others won't.
For your use I'd try to get a card that's clocked at near stock values ( certainly not the Gigabyte SOC edition ) but has non-reference cooling. What you want is a card that's not pushed to the limit and running cool. These are the most important in terms of GPU longevity and stability.