Very good attenuation can be expected With WY 1056. You may get better attenuation if you harvest the yeast. A OG 1.054 IPA I brew finishes at 1.006. The yeast will also stick to the bottom of the bottle when it finishes low.
Had to make my OG 1.052 amber ale wort less fermentable to get a 1.010 finish to better balance the hop and malt flavor.
I didn't harvest or use a starter, just smacked, shook, and let sit for 2 hours, then pitched. When I use it next time, if I get similar results I'll adjust my recipes.
Wyeast gives 73-77%. I have not gotten that high in my experience. I would also think it depends on the recipe. If you had almost all base grains and maybe some plain sugar added it would likely attenuate much more than say a Brown ale. If I like the beer, I don't really care what the attenuation was.