What OS are you running? Because XP only supports 2 or 3 GB of RAM, and since Dolphin is not made for OSX or vista, Im not sure it will use all of your RAM (not that it even needs 2 GB)
Also, 2x 8800GTX is a bit much, The Gamecube's Graphics card is from 2001. It prints low poly stuff at 640x480. The 8800 GTX is meant to handle extremely high poly situations, and print them at extremely high resolutions.
But like Toasty said, if the dolphin were optimized for quad core, 64 bit, and all of the Streaming SIMD Extension sets on your CPU, it would have more of an advantage over a 3Ghz single core CPU with the same amount of cache.