It's not going to be the highest performer compared to a top end GPU but it stands out for high hashpower for relatively little power use compared to most GPUs which deliver a similar amount of hashpower.Look up that article and you'll see what I'm talking about (though I wish I didn't forget the link to it as I could give it to you)

No GPU will be as efficient as an ASIC for scrypt mining but they're not widely available at a reasonable price yet so GPUs are still great for mining these coins