Make sure you have a beefy PSU for you rig as my rig pulls 620w from the wall with just 2 cards; idles at 100.
Keep in mind that because of constant power draw that mining requires that a good quality lower wattage power supply (e.g. 850W) is much better than a so so one that's much high (e.g. 1,000W).
For 4 7970 I think a good quality 1100W+ power supply is required.
Each card will draw 210 watts, so that's 840 watts on graphics cards alone. You should probably budget for at least another 200 watts for the rest, so 1.1kw sounds about right.