I partial mash, but I get around 75-80% depending on the yeast strain and extract brand. I have had very good luck with the extract AHS sells.
It's all about pitching a large starter (or equivalent amount of rehydrated dry yeast), providing the yeast with readily available nutrients and starting fermentation cool and letting it slowly rise during the last states of fermentation.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild