Nice system!
As a gaming build, you're practically maxing things out, currently (high res, single monitor)
.....though, I'm guessing that by your component choices you know this
Note that high res multi-monitor (especially 3d) can take a serious frame rate drop (even with 2x780).
How long will this give playable frame rates? than depends on many things such as just how much developers are willing to push the desktop market. You will definitely get 2-4 years of high-tier gameplay - and top-tier processor power for additional applications! "playable frame rates" would push this timescale further depending on your definition.
One thing to note.....you might want to increase your SSD capacity (it might 'look' unbalanced compared to the rest of your system). Even 120GB, though 'acceptable' for a gaming build, might be insufficient - especially in the context of your question. I would be looking at doubling this capacity for a nice bit of current and future headroom. I've been using a 240GB SSD for some years, and even with balancing application and game installs, I've had to invest in a second SSD, though everyone's requirements are different.
Note: my EX58 system is still going very strong, primarily due to its expandability and 'relatively future-proof' MB base. This should give you some confidence.