Ok, so I tried enabling Freesync for STO, but it caused the game to crash, and then when I tried launching with it still enabled it caused a full system freeze. (necessitating a hard restart)
After this happened, all of my framerates are somewhere between 1/2 and 1/3 of what they were before the crash, but only for STO.
I have tried removing the STO cache, clearing the AMD Shader Cache, verifying files, and varying graphics settings, all to no avail.
I used to get 75FPS average when running at 4k resolution, now I get 25FPS. I used to get 160+FPS at 1080p, but now I'm getting 81FPS.