  Models in extra-dimensions have unique features. Many of their surprising
properties simply result from the underlying 5D structure. This structure shows
up as ``Sum Rules'' involving the whole tower of Kaluza-Kleins. In this paper,
we present a holographic shortcut and derive these results without solving the
eigenvalue problem: we express 4D physical quantities directly in terms of the
5D metric. In warped space, one can go further and isolate the effect of the
new physics sector. This method can be used for any 5D model, and we apply it
here to the case of holographic QCD and technicolor.
