You can edit your own posts, so there's little need to make two posts in a row.
Anyway, I can only give advice on video files you've actually downloaded onto your PC rather than videos through SVPtube, but we might as well start there since it eliminates the internet connection variable.
First off, make sure that the video in question can actually play without issue when SVP is not running (right click SVP's taskbar icon and select "Exit")
1. In MPC-HC, try setting your output renderer to "Enhanced Video Renderer (custom presenter)", disabling "Accurate Vsync", and enabling "D3D Fullscreen"
2. If you do not have adequate video playback performance, set your decoder in LAVfilters to "DXVA2 (copy-back)"
3. If you still don't have adequate video playback performance, try setting your LAVfilters decoder to "Nvidia CUVID"
4. If still still do not have adequate performance, try setting your LAVfilters decoder to "Intel QuickSync"
5. If that still isn't enough, try setting your LAVfilters decoder to "None"
6. If after all of that and you still do not have adequate performance, then your PC hardware is either too slow or it is throttling itself.
Assuming that the video is running fine, please try the following if you haven't already;
1. Manually set the thread amount in SVP to a larger amount (try 15 and higher)
2. Make sure there is no file named "avisynth.dll" located in the same folder as mpc-hc.exe
3. Try disabling GPU acceleration in SVP; sometimes you can actually have a GPU bottleneck