Though the difficulty has increased once again. I have another miner myself of 200GH/s, and I am going to mine altcoins now, it's much more profitable. And because of the pool's system it will only mine the most profitable coin. And all the altcoins will be converted to bitcoins again.
What about the 2% pool fee of slush and the difficult increments over the next 3 month.. Your calculations are misleading please change them..