Poor responsiveness after changing RAM speeds--even after setting them back.

[lvcfr]

Main problem/TLDR:

• System unresponsive after playing with RAM settings--even after reset to last known good settings. How to fix?

In detail:

• RAM is supposed to support 2933MHz clock speeds, but defaults to 2133. I tried various XMPs and pre-made profiles from my bios. Before changing them, games ran mostly fine, and system responsiveness was good.
• When running my RAM at advertised speeds (2933), games perform much better, but slowly degrade to unplayable framerates. (Overwatch will start at 300 fps for the first 15 minutes, then barely over my monitor refresh of 165, then down to 100, then down to 50 fps. This is not acceptable.)
• When running at 2133 or 2400, I get more consistent performance in games without the FPS degrading over time issue.
• At this point in time, in both cases, system responsiveness is poor, even when using the last known good setting of 2133 with the timings that are supposed to be supported for that speed (according to hwinfo.)
• How poor? Sometimes, I wait 3-10 seconds for a context menu to pop up after right clicking. Discord freezes. Firefox tabs can freeze my whole system for several seconds at a time. This shouldn't happen with these specs (or any compute in 2018, for that matter.)
• Also, at the higher clocks, my system seemed to choose higher voltages (1.35v), which I believe is in spec, correct me if I'm wrong.
• When I have task manager open, and I do something that results in unresponsiveness, I don't notice any spikes on any graphs. CPU, RAM, GPU, and SSD utilization are all low, probably <1%.
• I have very few background services/apps running. Issue persists even a few minutes after a fresh boot without starting other applications.
• Components are about 7-8 months old now.

Specs:

• Ryzen 1950x
• Liqtech 360 cooller
• G.skill flare 64GB
• nVidia 1080GTX Sea Hawk
• Samsung 960 Pro (m.2)
• MSI x399 Gaming Pro Carbon motherboard (MSI MS-7B09)

What I've tried so far:

• Using the two included XMP profiles.
• Using MSI's "Memory Try It!" profiles.
• Manual configuration, tried higher clocks with both supported timings, and looser than supported timings.
• Resetting RAM to last known good settings in bios--which for me is just "auto" on everything.
• Checking thermals. They seem good. CPU is under 70 under load, idles between 55 and 60ish.
• GPU thermals are similar.
• Tried using legacy compatibility mode (8-core mode)
• Local memory mode
• Rebooting
• Cinebench r15 gives me a score of 1487 or so. However, userBenchmark says my system's RAM, CPU, and GPU are under-performing slightly relative to benchmarks of the same part (I think)
• Clearing hard drive space, not sure if having 100GB of 500GB free is an issue.
• Checking SSD health, Samsung Magician says it's all good.

What I might try next:

• Reseating RAM
• Memtest
• Virus scan
• Windows update
• SSD firmware update
• Motherboard firmware update
• Local memory mode with the higher clock speeds, maybe also try distributed memory mode and see if the problems will go away with any of the RAM speeds.
• Reinstall windows (really don't want to do this yet.)
• DDU my GPU drivers and update them again.
• Page file settings?

Got any other ideas? Or maybe advice on which things I should prioritize first when troubleshooting? This is driving me insane.