The Lian-Li cases around that price are good too if you want something understated. Won't get as much in terms of features or capacity but the build quality is second to none.
I don't know where you've been reading that FreeSync is better than G-Sync. FreeSync can be adopted by multiple vendors as it's just an implementation of the variable refresh rate specification as part of DisplayPort, and the monitors are cheaper, but that's about it. G-Sync is proprietary, yes, but if you buy a high refresh rate monitor with G-Sync, you know the G-Sync range is going to extend to the monitor's highest refresh rate. There's also stuff about latency however in practice there isn't a difference really.
Unless you have a specific need I'd stick with the 390X in that build, purely because you're getting better performance for less cash.
Others may be able to provide input on this, but I've found that even with G-Sync, <55fps or so still feels pretty horrible (that said, maybe that's just me - I always ensure my frame rate doesn't dip that low). From my experience it's the combination of high refresh rates and perfect frame syncing that makes variable refresh technologies shine.