NEFFMen's Daily Beanie, Warm, Slouchy, Soft Headwear

Q: how much does this stretch?

It all depends...I own several of the Neff Daily beanies and some stretch more than others. Haven't really figured out why either

Q: It looks like some of them are different lengths. Is this just how the item is pictured, or do different colors have different lengths?

Different colors are the same length, however there can be some variance from beanie to beanie. If so it should not be a significant difference. If you looking for more length try the Daily Fold, it is made to be worn folded and unfolded in which if you unfold it is longer :)