You only have a limited time to get some profit out of your hardware before a newer generation of mining hardware is released that makes your models obsolete (and worthless). So at the minimum, you should not only be making back the $5000 but also enough to buy up a newer batch of hardware within the next year or so.

Which looks simple on paper, but profit isn't linear in practice because of the fluctuations in global hashrate and the delay in adjusting the mining difficulty.