Running an update operation using
 

{
  findAndModify: "coll",
  query: {_id: 1},
  remove: false,
  new: false,
  upsert: true,
  update: {
    $addToSet: {
      values: {$each: [value1, value2 ... value600]},
    },
  },
}

 
will check each value in the array against the entire current content (see addToSet)

This doesn't scale and cause higher contention rate with similar operations occurring on the same object