An FX-8350, even at stock, will not bottleneck the R9 390x. And, while an overclock could POSSIBLY provide a performance increase in some CPU intensive games, it will likely be minuet and barely noticeable.
The only way to determine if there is a bottleneck would be to put a weaker card in your machine and see if it performs the same or worse. If it's the same, then you've been bottlenecked. 4.6GHz vs 4.5GHz is like driving 46mph versus 45mph - do you get there faster? Sure, but you won't notice it.