Instead of getting a new card, why not get a better CPU, if you wanna stick with your motherboard, get a 8350 or something. Or if you want to really boost performance, get an i5. The r9 380 is a bloody great card and if you pair it with an i5 you will have quite the gaming rig. AMD Cpus can't even come close to intels without overclocking the crap out of them (which means decreasing the life of the chip and having to buy better cooling). I have an 8350, its pretty good for the money, but I swapped out to a i5 3570k that I got quite cheap. Haven't looked back since.
And also, crossfire isn't actually that great, not many games have proper support and optimisation for it, the cards will heat up a LOT so you will need to probably add more fans to your case. And for some people (like me
) it's a bit of a bitch to get set up. My crossfire option wouldn't even appear in my Catalyst/Crimson drivers and I had to keep resitting the cards and rebooting. In most of the games that I played, there was little or no performance increase as the games lack proper support. In a lot of games you will find microstuttering with inconsistent frame rates.
In games that had proper support the boost wouldn't be that great. For example: 60fps with one card, 80-90fps with two. AMD still has a long way to go with Crossfire whereas Nvidias SLI is known to have far fewer problems due better drivers.
But it all comes down to how much you want to spend and the prices in your country
Edit: Just read that you have a MSI 970 board, it's quite the good board, so you would probably be better off getting a 8350 as you can get them for a pretty good price now days. Because if you switch to intel you would have to get a new board and cpu which will be costly. The 8350 is defs better than the 6300 but I'm not sure by how much by.