I don't really have any experience with the boot cuts. In terms of stretching, I'd say they stretch a bit but probably not an entire size. What is the make up of the jeans? Also, washing them in hot water may cause shrinkage and will likely cause the wash to bleed. If you do decide to keep them and get them hemmed, I would say to wash them first, so they shrink a bit and then get them hemmed. If you air dry and wash cold, you'll avoid a lot of shrinkage.