I'm not very familiar with AMD systems, but from the looks of everything, it looks like a pretty balanced system. Any reason you are asking about a bottleneck? Are you experiencing stutters or something? You didn't put what OS you are running, and that could have something to do with it as well.
Honestly, short of a whole new build, I think you are pretty much set. Is there any reason you think you need to upgrade? Everything you have is about as good as it can be for the system you've shown really. You should be able to play any game out there on max or near max setting for at least the next year.
If you seriously want to upgrade, I'd say a new mobo, processor (although that processor is fairly capable), and RAM. If anything the RAM is the weakest link in the system, but not by much and it is pretty much the fastest RAM that you can put in that mobo. But that really isn't an upgrade in my eyes, more like a whole new build.