Super Mario Galaxy slow down when sun/lens flare is on screen

[degasus]

They check if anything was rendered in front of the sun. This check read back a value from the final framebuffer. This operation is quite fast on the Wii, but very slow on current systems as it serialize the CPU emulation and the rendering. You might check if your GPU is forced into high power mode. Nvidia tend to downclock on low usage. And this is a low usage on average, but with an high peak performance requirement...