V- sync causes massive framedrop

[Dolemub42]

This is the way v-sync always works if your computer can not maintain a steady 60 FPS. It is not specific to Dolphin. If you actual framerate is less than 60 FPS, say, 58 FPS, with v-sync enabled it will automatically switch to half-refresh hence 30 FPS. This is inherent to the way v-sync works. The only work around is to use a technique called tripple buffering in conjunction with v-sync, which is supported by some PC games and third party apps but not Dolphin. Also, some monitors support an nVidia feature called G-Sync which is a hardware solution hence circumventing the need for software v-sync and its limitations.

What you can try:
1) Play around with settings to give you better FPS overall, which will reduce or eliminate any drops below 60 FPS. This is the best solution. Or upgrade your hardware, specifically CPU.

2) Try the DirectX 12 backend, if your graphics card supports it.

https://forums.dolphin-emu.org/Thread-unofficial-dolphin-dx12-backend
or
https://forums.dolphin-emu.org/Thread-unofficial-ishiiruka-dolphin-custom-version

3) Adaptive v-sync, which will enable v-sync when 60 FPS is maintained and dynamically turn it off in instances when it drops below 60 FPS. This works well with PC games, but I can not guarantee that it will work with Dolphin. Some programs like RadeonPro allow enabling triple buffering in PC games, but this has never worked well for me with emulators.