Well that means they've refined it quite a bit, that's good to hear. Though are you sure you've increased the internal resolution and you're not just stretching it? My GPU is a 6970 at 1GHz, it does just fine.
It's an emulator and it doesn't work like a native program. The AA in those emulators, especially Dolphin, is kick to the CPU's balls rather than the GPU. The load from the AA to the GPU is negligible so long as the GPU is a powerful one.
It's strangely done, the AA is so heavy on the CPU that I'm better off just rendering it at a much higher resolution (4 times native) and letting it downscale for an AA effect rather than use its MSAA. My CPU is close to maxed, while the GPU doesn't even reach 40% usage.