I'm farming for one aswell. What ive noticed, is that the rate white items drop aren't THAT game-changing with mf gear on. Plus you find goodies on the way, then. So I stuck with MF.
But for tips... IDK, Ive searched a long time aswell. Cows should be great for threshers, but perhaps not GPA/GThresher. Mob density.
Otherwise Pits, ancient tunnels, chaos sanctuary any works. I havent really bothered with LK, since it seems so random with monster spawn etc. At the moment got 1 rack dropping colossus voulge, meh. the chest layout is topdog so cannot roll out of that.