680 watts looks to be the combined total of all the positive rails, looks like a minimum of 45 amps combined on the 12v, which will increase to who knows what depending on the 3.3 and 5v loads.
Most places do say between 55 and 57 amps total.
675W is the combination of all the positive rails, but the positive rails that are not 12V rails (+3.3V and +5.0V) are rated 155W. So in theory that would leave a minimum of 520W to the 12V rails, which would leave 43A to the 12V rails.
How old is the Epsilon. I think your borderline. If your planning on running a o/c i5 750, I would use that or any reason to maybe get a high quality , single rail 750+ psu. In the end its to power maybe the most power hungry single gpu ever