7770 crossfire

I have 2 xfx 7770 black editions in crossfire. It gives me around a 60-80% performance improvement over a single 7770. Does anyone alse has crossfire/sli setups? if so how much performance do you gain?

I have got a single 7770, its speedy enough for me.

But there is a video on youtube, where 2 7770`s in crossfire get about 100-120% performance over a single card!