Well, there are so many people who are doing what you are doing right now - buying high hashrate ASICs.  Because of this the the amount of hashing power is increasing rapidly.  When the current rush of miners have got their systems in-hand, the hash rate will steady out somewhat.

Unless the price of bitcoin increases, I don't think rigs bought now will ever make enough to repay their cost as the total hash rate spirals.

Of course, you could keep buying more rigs to keep up your hashing power