This. But the goal should be to keep the overall form of the tree as good as possible. I.e., don't crape murder it. That might not reach your seven foot goal depending on the height of the tree now, but trimming is something to be done surgically and thoughtfully, in my opinion. I personally value the form of a tree above many other criteria when it comes to trimming. Even a blooming tree only has flowers for a few months out of the year. The rest of the time, you see its branching structures. Crape myrtles have a particularly unique structure that I think, when thoughtfully pruned, can be highlighted.