Tl;Dr: it's enough
You want to have around 250-300% mf, since diminishing returns kick into high gear after that. You should always aim for kill speed > mf, no matter at what point you are, but definitely after you got around 250 mf. Here's why:
Killing a monster with 1000 mf in 10 seconds gives you a "real" increase of finding a unique item by 400% iirc (this is an increased chance, not a "gain unique item with a 400% chance")
Killing a monster with 250 mf in 1 second gives you a "real" increase of finding a unique item by 200% iirc.
So if you kill 1 monster, the 1k mf setup wins. But if you get to kill 3 monsters it'll take you 30 seconds with the 1k mf setup but it'll take you only 3 seconds in the 250 mf setup, meaning you get far more killing done and thus have a much higher chance of actually finding a unique (remember: you only get items if you kill enemies :D)
You could opt to switch your weapons right before a kill (say a boss) to an mf switch if it makes you feel better (isted Ali babas, 6x isted sword, gull along with an isted monarch).