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.
Jeff Gladish, Tampa (989.3, 175.1 Apparent Rennarian)
Homebrewing since 1990
AHA member since 1991, now a lifetime member
BJCP judge since 1995