All the way to the ceiling.

Are you wanting backsplash just for the countertop areas? If so, I think it would depend on the material chosen for the backsplash. If your going with glass all the way to the bottom of the upper cabinets. If your going to go with a stone backsplash, I think either a 4" tall backsplash or again all the way up to the bottom of the upper cabinets.
Can you post a picture?