Interesting. At 1.15BTC/5GH, if these are up and running by the beginning of October ROI is 3 months, but if they are up by the end of October they will never ROI.
I am not sure how you are doing your calculations but you are not taking into account the increase of the price of BTC based on the increase of difficulty. It is a direct correlation that is delayed by a period of about 6 months so these systems will definitely be profitable.
-Adeel
that is a good calculator that try to forecast mining profitability in near future: try it... it's nice