Do you still get the consistent slowdowns with 1x IR? If so, that means that the bottleneck is probably your CPU (your CPU is the limiting factor which prevents you from getting full speed).
As for the random slowdowns, that's stuttering caused by shader compilation (see link above). There will be less stuttering as you play through the game because the shader compilations (that slow down the emulation and are responsible for the stuttering) only happen once. The wiki explains this much better than I do, so here's a quote:
As for the random slowdowns, that's stuttering caused by shader compilation (see link above). There will be less stuttering as you play through the game because the shader compilations (that slow down the emulation and are responsible for the stuttering) only happen once. The wiki explains this much better than I do, so here's a quote:
Quote:Metroid Prime 3: Corruption (Wii) is one of the most susceptible titles to shader compilation stuttering. The GC and Wii have no concept of shaders - everything is executed directly by the hardware without an intermediate programming language (API). Modern computers and mobile systems do not work in this way, requiring the use of shaders as an intermediary so your system's GPU can perform the tasks that the GC and Wii GPU performed directly. Shaders have to be generated though, and since GC/Wii games are not designed to create shaders ahead of time as a PC game would, when a new effect appears Dolphin has to delay the CPU thread while the GPU thread performs the compilation; a pause that does not exist on the consoles. For most games shader generation takes only a few milliseconds, but for a few demanding titles, the shaders that they generate are so large that they can result in noticeable stuttering, in severe cases pauses of over a second may occur.(emphasis mine)
Eventually stuttering will reduce as a shader cache is built up, but there is no solution to this problem at this time. Changing your GPU, updating your GPU drivers or updating Dolphin may invalidate the shader cache, requiring it to be rebuilt from scratch.