No on truly knows how ML effects drops. (besides njaguar)
This is the only information provided to us.
Quote (Ladder Slasher Portal)
+ Magic Luck Increases the chances for higher stats on an item drop.
You must also take into consideration -- Group vs Solo; Speed vs ML; and overall survival-ability.
If you have trouble killing the well mobs with your normal gear, i suggest not stacking ML. If not, go for as much as you can.