I don't usually brew many beers above 1.060, but generally speaking I'd start using extract once my mash tun can no longer accommodate the grist at 1 qt/lb. BeerSmith makes it pretty easy to figure out.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: Dark Mild w/ 002, Dark Mild w/ 028, sLambic II, Flanders Red II
Primary: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, sLambic I
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Huell Melon Pale Ale
Bottled: Flanders Red I