I never considered Wii emulation but I have played with Dolphin for GameCube emulation off and on quite a bit. I notice that reports and results are mixed, supposedly people with machines inferior to mine claim to get full speed and perfect emulation yet I never get either. Then people with machines more powerful than mine claim they can't get it to do crap. Emulation is such a mess anyways but I think that Dolphin especially is just trying to be more than it should, they should have split it into two different projects and left it alone.
As for what works and doesn't work I can say that my results are mixed but for the most part apparently CPU speed matters most as does what instructions said CPU can handle. I understand video cards have little to do with it.
As for the legality of ripping vs downloaded, screw it you bought the game do what must be done.