Originally Posted by MageB420666

It mainly depends on whether the object is going to stay in one peice one entry into the atmosphere or shatter into thousands of smaller pieces. Once the object reaches a certain mass it doesn't matter what it's made out of, if it hits the Earth, say goodbye to humanity. But if the object breaks up into thousands of smaller pieces, it may devastate a large area, but it won't have the same effect as one huge piece.