Are they purple from toe bang or just from being real tight? Unless it's because of toe bang I wouldn't size up, I size to a 28.5 but wear a 26.5 and lose my big toe nails all the time (and yes the boots fit my feet, I never have any actual pain). Especially with a full tilt, what you perceive as tight now will get comfier later, and what you perceive as comfy now will be sloppy later. Just some food for thought.