The overall length shouldn't matter too much as long as it folds over nicely.
You want the top third to be pretty flexy and bend away when you have a fish on.
Look at standup game rods, the tops fold away and give the user a much shorter lever when a fish is on. You want your beach rod to do the same but on an overall longer scale.
The length really is only there to cast out and hold your livey. Once a fish is hooked you don't need or want that length. So you want a strong butt with a really supple top section.