My calculation is 12 months to recoup assuming no difficulty change and stable ETH price, with a 5x 1070 rig. I get free electricity, so maybe 14 months with that included.
I agree that GPU prices are frustrating, though.
The problem with that assumption is do you really believe that difficulty will not change and that the ETH price will remain stable for 12-14 months?
This is the problem of all those calculator sites in that for them to even work for predicting much more than a week out they rely on those two assumptions to hold true, when in fact the reality is often the exact opposite, or that difficulty will continue to rise and the coin price will not be stable, probably go down during the next 12 months. This is much akin to weather forecasting, where short-term 2-3 days they have a good track record, but expecting a forecast a few weeks out to match up with what they say it will be today is very unlikely.