There's no mf cap, if you're doing pindle/meph more is better, if you're doing pit/cs/baal/etc. then put on more kill gear to speed up clear time (you should be at like 300-400 depending on class for these), if you're a barb weapon swap to hork.
High mf does not mean you'll always get drops, it's random and sometimes you get nothing for a long time.