If this is as powerful as Gamecube, that should already answer your question. As a general rule of thumb, you need the power of a console 2-3 generations ahead of the console you want to emulate, unless you have slightly more powerful and share MOST of the same hardware and/or architecture. Gamecube and Dreamcast are the same Generation, so something as powerful as a Gamecube can have games with just as good quality as Gamecube and Dreamcast games (if you find a homebrewer with the talent and the drive to make one such game) but not the power to emulate Dreamcast.
As for Saturn, that's only 1 generation before Gamecube, not to mention, it's a damn tough system to emulate, from what I've heard.
-God Ginrai