We present an algorithm for simultaneously finding a Rectilinear Steiner Tree T and buffer insertion points into T. The objective of the algorithm is to minimize a cost function (e.g., total area or power) subject to given timing constraints on the sinks of the net. An interesting side-effect of our approach is that we are able to derive an entire cost/delay tradeoff curve for added flexibility. The solutions produced by the algorithm are optimal subject to the constraint that the routing topology be induced by a permutation on the sinks of the net. We show that high quality sink permutations can be derived from a given routing structure such as the Minimum Spanning Tree. This derivation provides an error bound on the minimum area solution induced by the permutation. The effectiveness of our algorithm is demonstrated experimentally.