High mf is typically for farming 1. Act bosses, say at the beginning of a ladder reset to self find progression gear (unique and set items) or 2. Lvl 85 areas for hard to find uniques like fathom, griffon, etc.
If you are looking for runeword bases then you should have 0 mf and be looking in high density areas like cows and chaos.
Most end game setups can have around 100 mf (enigma + gheeds) so you will find a nice mix of both socketables and rare/unique items.
If your goal is only to find the highest fg sellable items I'm not sure the best way to do that, other than playing in high player count games so more items drop, in which case killing speed > mf.