Go back and maybe listen to Matt from Firestone on CYBI when he is discussing Union Jack? He recommended the White Labs equivalent and they do a modified step mash at 144-146F and then raise to 158F, I believe. He also gives their fermentation profile and I am pretty sure their attenuation gets close to your desired goal. It may be worth visiting. It's been awhile since I listened to that episode, so don't remember it exactly...
Firestone Walker may be getting good attenuation because of their Burton Union system. That would certainly keep the yeast in suspension.