I'll be brewing a porter with this yeast later today, washed from a previous batch. This will be the first dark beer I've brewed with it, though it has always performed very well for me in the past with my bitters and browns. I've been getting around 75% attenuation.
This is not a highly attenuating yeast to begin with and it does best with a big, healthy yeast pitch and lots of oxygen. Of course, attenuation will also be determined by recipe, mash temp, and fermentation technique.
