Your main enemy here is going to be when you put those 7970 beside each other. I would almost say you would need a water block at least on the middle card or else you're going to have them start throttling due to heat. I have two of them in one case and side by side the top card would max out at 97 and the bottom at 92 once I put a space between them they both I was getting 88 and 86 for temps. This was without over clocking.

I like this calculator http://www.bitcoinx.com/profit/

as it is pretty accurate even though it was not designed to give profit for a pps pool. Just put in the cost of your mining hardware and your hash rate.