Its a much debated topic but here are the facts, and this is why I said replacing it with an i5 would be okay too. Firstly the i5 has much better single threaded performance while the FX has much better multithreaded performance. For this reason the FX excels in non-gaming applications while the i5 excels in traditional games. However there is more to it then that. In games not optimized for multiple cores, which are most currently on the market, there is a minor difference in frame rates(~5 fps or so). A couple, like planet side 2 and skyrim heavily favor the Intel chip(>10fps). For the games with minor difference it isn't really relevant because it will not impact playable settings and could be fixed with a good OC. As for skyrim and planet side, if you play those games avidly then Intel will perform better, even though OCing will help a lot. Some games perform equally or favor AMD(BF3/4 and Crysis 3 are examples). These games in some way show the future. Since you don't want to upgrade for a long time you will see more of these type of games. I have a couple links to demonstrate that devs will be coding for AMD and believe the FX has a better future as a gaming chip:
http://www.eurogamer.net/articles/digitalfoundry-future-proofing-your-pc-for-next-gen
http://www.playstationlifestyle.net/2013/08/05/the-ps4s-big-challenge-is-its-amd-chip-that-heavily-relies-on-multi-threading-says-planetside-2-dev/
The second link if from the plantside devs, a game heavily optimized for Intel. In other words, current games favor Intel's architecture a little, but this is bound to change in the future as devs pick up the tools to properly code for many cores. Hope this helps