If and only if you have truly free power would i even come close to that power hog of a card. At the price you quote it has about a 5 month ROI before you make any profits.
Yeah power is truely free (but only for 1 rig max ) , Just like to know whats are the hashrates of this card , and how much likely is it that it burns or melts something due to power consumption
7990 is good for mining ZEC.