The sound problem is related to the slowdown. Your emulated Wii generates too few samples, so it will stutter...
Bad luck, there are only hacks to improve the CPU performance. But I guess your bottleneck is the GPU. Just to be sure, you render at native resolution?
You can try to use the custom build in https://forums.dolphin-emu.org/Thread-unofficial-ishiiruka-dolphin-custom-version . This fork tries to merge as many improvements of the official dolphin tree, but it has skipped an accuracy improvement which increased the GPU requirement a lot. So it may be perfect for your requirements. The downside: Bugs, less tested, experimental, might kill kittens, ..., please don't report issues with this build anywhere in this forum but in this single thread.
Bad luck, there are only hacks to improve the CPU performance. But I guess your bottleneck is the GPU. Just to be sure, you render at native resolution?
You can try to use the custom build in https://forums.dolphin-emu.org/Thread-unofficial-ishiiruka-dolphin-custom-version . This fork tries to merge as many improvements of the official dolphin tree, but it has skipped an accuracy improvement which increased the GPU requirement a lot. So it may be perfect for your requirements. The downside: Bugs, less tested, experimental, might kill kittens, ..., please don't report issues with this build anywhere in this forum but in this single thread.