If you're trying to use SLI with Dolphin, don't. I don't know how SLI is configured but if you can turn it off for Dolphin, do so.
Also, are you actually turning every setting in enhancements up to it's highest? If so, you don't want to do that. Set your internal resolution to something that closely matches your display's resolution, and then set anti-aliasing to your liking. With your hardware I don't see why you should have issues with 4x SSAA, but 8x SSAA is damn hard to push regardless of your hardware.
Also, are you actually turning every setting in enhancements up to it's highest? If so, you don't want to do that. Set your internal resolution to something that closely matches your display's resolution, and then set anti-aliasing to your liking. With your hardware I don't see why you should have issues with 4x SSAA, but 8x SSAA is damn hard to push regardless of your hardware.