Have you considered using one of the FX8320E processors? They might be slightly cheaper. Otherwise a 6 core FX CPU should be fine.
The first thing you should do is go to your mobo maker's website and see what CPUs are supported by you specific model and Rev. mobo. You may need a BIOS update before installing whatever new FX processor you choose. The website should list the minimum required version BIOS for each model FX CPU.