Quite frankly, using a GPU rig to mine Bitcoins is only for people with FREE electricity, fully paid for hardware, and no way to sell the hardware. You would almost certainly make more money by selling the hardware, than it would ever return by mining.
Even with free electricity mining BTC with a GPU is a horrible idea. You can get a USB stick miner that will outmine the GPU all day long.
Really do the math but don't mine BTC with GPU unless done for a short time just for learning.