From memory the 295x2 is a 300W+ GPU. Six of them would be 1.8kW. You would need to have a dedicated circuit build just for that system to have that run. You could run 5 of them ok, but 6 would be too many.
Bitcoin has gone up in value some so it might be worth it, but considering how slow a GPU mines bitcoin it probably isn't. Litecoin or some other such coin might be worth it. Though the value per coin is a lot less.
Edit: According to the first result I got from a web search, I'm going to use his .15/kWh for this math. He said the "avg" is .13, but your 1.8-2.0kW PSU is going to be pulling more than 2kW from the wall and that's what you have to pay for. So hopefully this all "avgs" out. If it's .15 per kWh and you are...