TheFriendlyHacker

Just to do my due diligence and mark this thread as "solved":
 
Yes, the Asus Sabertooth 990FX R2 can most certainly handle an FX-9590 chip with no problems whatsoever. 
 
However, upgrading from an FX-8350 to a 9590 is not recommended IMO, since an overclocked 8350 can match or surpass the 9590. 
Ultimately, my solution was to upgrade to Ryzen. And ever since then, I haven't had any unexpected troubles with FPS. 
 
Although, I think I should answer the question I originally asked, in case anybody else encounters the same problem. 
Based on what I have read (and experienced, I suppose), modern games often don't take full advantage of FX chips. So even though there is quite a bit of CPU power available, the games just won't use it for whatever reason, leading to significant bottlenecks. 
Now mind you, the FX-8350 (with my experience) is absolutely capable of running most games fairly well...depending on your standards and budget. I'd still recommend it for those who need a budget PC that doesn't completely suck at gaming. But for those who are wondering why their FX chip isn't performing as well as expected, that's why. 

My other specs are:
- Ryzen 5 2600x
- GTX 1070
- MSI B450M Tomahawk 

All of those parts (including the RAM) were purchased together and assembled into this PC when it was built (in late 2018). And everything worked fine until now. Given there have been no significant hardware changes (aside from swapping out the secondary 1TB HDD with a 3TB one a few months ago), I can't imagine anything suddenly changed that caused this (although you may have some experience that I don't)

Lemme try it with just one 8GB stick rq, I will report back. 

I also suggest the Meshify C. Have one myself and the airflow is excellent 

The Lian Li LANCOOL II-X is a pretty good case, it support up to 8 fans (2 top, 2 bottom, 3 front and 1 back) and support up to a 388mm long graphics card which should be enough for nearly, if not all graphics cards out there. It also comes with 3 120mm fans included and has a little RGB as well.
https://pcpartpicker.com/product/kRFKHx/lian-li-lancool-ii-x-atx-mid-tower-case-lancool-ii-x

I (finally) got my Ryzen setup complete about a week ago, rocking an R5 2600x on an MSI B450 mobo. 
 
I've been trying to set up an Ubuntu VM on my machine using VirtualBox. However, I keep getting an error that "AMD-V" is not enabled (I assume that means virtualization in general is not enabled in my BIOS). So I took to the Google to try to find out how to enable it. But. The answers I found either 1: didn't answer the question of "how to enable virtualization on MSI B450", or 2: were for a different motherboard entirely. 
 
So. Does anybody here know where in the BIOS on an MSI B450 I can enable virtualization? And does this board even support virtualization?

deocding videos is handled by a different part of the GPU, so as long as you dont let the GPU hit the power limit it wont affect performance.

If the driver is buggy and don't do what it's meant to do, then maybe.

I did double-check the cooler awhile back and even re-applied the thermal paste, so no dice there. 
 
Thank you all for the replies! I'm thinking I'll just let it run hot. Even if it does reduce the CPU's lifespan, I'll likely have upgraded by the time it kicks the bucket. 

In the future, use pcpartpicker.com to get access to all websites when comparing.

I finally did it. I've upgraded to Ryzen  
 
Like I said, I've been considering doing it for awhile, but this post was kind of the "final straw" if you will. And after selling my AM3+ hardware, I only netted a loss of ~$160. Needless to say, the new R5 2600x handles games (and everything else) much better than yee old FX-8350. 

Just to do my due diligence and mark this thread as "solved":
 
Yes, the Asus Sabertooth 990FX R2 can most certainly handle an FX-9590 chip with no problems whatsoever. 
 
However, upgrading from an FX-8350 to a 9590 is not recommended IMO, since an overclocked 8350 can match or surpass the 9590. 
Ultimately, my solution was to upgrade to Ryzen. And ever since then, I haven't had any unexpected troubles with FPS. 
 
Although, I think I should answer the question I originally asked, in case anybody else encounters the same problem. 
Based on what I have read (and experienced, I suppose), modern games often don't take full advantage of FX chips. So even though there is quite a bit of CPU power available, the games just won't use it for whatever reason, leading to significant bottlenecks. 
Now mind you, the FX-8350 (with my experience) is absolutely capable of running most games fairly well...depending on your standards and budget. I'd still recommend it for those who need a budget PC that doesn't completely suck at gaming. But for those who are wondering why their FX chip isn't performing as well as expected, that's why.