Since you have a pretty decent budget to work with, I'd definitely recommend switching platforms now.
You already have an OC'd 8120, so going to an OC'd 8320 isn't going to give you a huge gain. Going to an OC'd Intel 4770K, however, will give you very substantial gains over any AMD FX setup. Plus, the 4770K consumes half the power of the 8320, so you will not need to upgrade your power supply.
Just look at the tremendous power consumption difference between Intel and AMD. Then take into account that the Intel 4770K is faster and will be at max load for a shorter period of time to finish a certain task, and the difference becomes even larger.
As for motherboards, I would recommend the Asus Z87-A:
Or if you want to spend a bit more, the Z87 Pro has upgraded VRMs, not that it's really necessary for Haswell since it's so efficient compared to FX:
If you want to do a smaller build but still crossfire 7970s or 280Xs, the Maximus VI GENE is also an excellent board:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131975Edited by 996gt2 - 4/15/14 at 7:00am