Emulator

Okay, I'll do that when I get back to my desktop, and then I'll try earlier stable/development versions if it doesn't help. I'll let you know what happens.

Vsync doesn't appear to have been on. I tried some earlier versions, and they don't work much better, so I guess it's not a regression.

So, it's very possible that a few things are happening.

1: The songs are just slow, a graphical feature in them is very slow. Maybe try checking disable EFB Access to CPU?
2: Something in the JIT/Interpreter is extremely slow?
3: The game is just demanding/uses a feature that we can't emulate well.

Maybe someone with a profiler can check it out?

1. I tried disabling efb copy, and that didn't seem to help much if at all, plus it caused big black boxes to cover parts the screen occasionally.
   2 and 3. Guitar hero Metallica runs perfectly, and I would think that it should be equally or more demanding, but I don't know.

Have you tried the GPU part of the Laptop Performance Guide? This might just be GPU throttling bullshit as usual. https://forums.dolphin-emu.org/Thread-unofficial-laptop-performance-guide

No, that's not it. It's a desktop, and it only uses the gtx 780.

Is there some kind of hack that would prevent dolphin from rendering the animation of the stage and band in the background, and only do the notes? That might be worth a shot.

I have Guitar Hero III - Legends of Rock now and tested through the game. I'm unable to reproduce any kind of slowdown throughout the song. There are camera angles that are more demanding due to EFB Copies being used for effects, but that would come down to a CPU performance issues.

I'd like to make sure I have the right version of the game before proceeding forward and doing more research though.