Optifine

You can overclock and tweak your PC all you want, the simplest and most important things to check are in-game settings:

Make sure Fast Render turned on if you struggle with your FPS, this is the most impactful setting for performance,
If you don't mind, disabling Custom Sky will help a bit.
Putting Render distance to 4 is enough for practice in my opinion.
If you don't have a good GPU, consider playing in 1280x720, it can significantly increase performance.
You can turn on Smooth FPS to lower Minecraft's GPU utilization (e.g to leave more for OBS' NVENC usage)

Video Settings
- Graphics: Fast
- Render Distance: 4-8
- Use VBOs: ON
  - In newer versions of the game, VBOs are on by default and cannot be toggled off.
Performance
- Smooth FPS: OFF
  - Turning this on will lower framerates can help with OBS performance issues if Minecraft is taking too much resources. (todo: see if this improves frametimes)
- Fast Render: ON
  - Having Fast Render on will disable shaders on 1.7 to 1.12. This includes Motion Blur, Menu Blur, and Color Saturation.
- Fast Math: ON
- Render Regions: ON
  - OFF if you are on an integrated graphics card, including Apple silicon.
- Smooth Animations: ON
Quality
- Antialiasing: OFF
- Anisotropic Filtering: OFF