Next diff adjustment (eta 2.5 days) you can expect to earn $405 per month (at the current btc price 688 which is likely to go lower still). If you pay with btc you _may_ break even in 3 months.
Um, no. $700/BTC, diff 910 million (2.5 days from now. You cannot get these cards before then), 30 day period, 25GH/card: you will earn $300. But guess what what: we will see at least *TWO*, and perhaps *THREE* difficulty increases during that 30 day period. So your true earnings will be significantly less than $300. Closer to $200. Not sure how you are getting $405. Sure, we can assume a best-case hashrate of 35GH/card. So instead of earning $200 in 30 days you will earn $250.
I think it is pretty clear that these boards are unlikely to earn back their $1000 purchase price. Not in BTC, and not in fiat. Not unless $/BTC goes up significantly. But if you think $/BTC will go up, you are better off buying coins directly and holding. If you think $/BTC is going to go down, this deal becomes even less attractive.